Authentication apparatus and method

ABSTRACT

An authentication apparatus operative to determine the authenticity of an item comprising a film substrate responsive to detection that a portion of said item located in a measuring region of said apparatus has a predetermined birefringence characteristic, said apparatus comprising: an item detection arrangement operative to determine if at least a portion of an item is located in a measuring region of said authentication apparatus; and an optically-based birefringence measuring apparatus, wherein said authentication apparatus is operative to compare a measured birefringence characteristic with a predetermined birefringence characteristic and to produce an authenticity signal indicative of authenticity or otherwise of said item based upon said comparison, said apparatus further comprising a control means operative to control output of said authenticity signal from said apparatus responsive to determination, by said item detection arrangement, of presence or otherwise of said at least a portion of said item in said measuring region.

This application is a national stage application of International PatentApplication No. PCT/EP2013/071435, filed Oct. 14, 2013, which claimspriority to Great Britain patent Application No. 1218463.6, filed Oct.15, 2012. The entirety of the aforementioned applications isincorporated herein by reference.

FIELD

The present invention relates to an authentication apparatus and method,and particularly, but not exclusively, to an authentication apparatusfor and method of authenticating an item comprising a polymer film.

BACKGROUND

Polymer films are increasingly being used as substrates in fields wheresecurity, authentication, identification and anti-counterfeiting areimportant. Polymer-based products in such areas include for example banknotes, important documents (e.g. ID materials such as for examplepassports and land title, share and educational certificates), films forpackaging high-value goods for anti-counterfeiting purposes, andsecurity cards.

Polymer-based secure materials have advantages in terms of security,functionality, durability, cost-effectiveness, cleanliness,processability and environmental considerations. Perhaps the mostnotable amongst these is the security advantage. Paper-based bank notes,for example, can be relatively easy to copy, and there is loweroccurrence of counterfeits in countries with polymer-based bank notescompared to paper-based bank notes. Polymer-based bank notes are alsolonger-lasting and less-easily torn.

Security materials based on polymer films are amenable to theincorporation of a variety of visible and hidden security features.Since the introduction of the first polymer bank notes approximately 25years ago, security features have included optically variable devices(OVD), opacification features, printed security features securitythreads, embossings, transparent windows and diffraction gratings. Asidefrom complicated security features there is also the more immediateadvantage that the high temperatures used in copying machines will oftencause melting or distortion of polymer base-material if counterfeitersattempt simply to copy secure materials (e.g. bank notes) using suchmachines.

However, standalone apparatus suitable for the authentication ofsecurity documents at points of sale is only in limited use at thepresent time. Points of sale may have a UV light source for detecting afluorescent ink on a bank note, or a pen which does not mark authenticbank notes. These devices do not provide a high technical hurdle tocounterfeiters. Points of sale may also have electronic apparatus whichauthenticates a credit or debit card using a tamper-resistant electroniccircuit embedded in the card. However, this apparatus is complex andexpensive, requires time to process and a telecommunications link to aremote server, and is not suitable for use in the authentication of banknotes during routine cash transactions.

More sophisticated apparatus for checking the authenticity of bank notesis in common use by credit institutions and professional cash handlersfor checking bank notes which are to be returned to circulation, butsuch apparatus is expensive, particularly as it is generally necessaryto check for the presence of multiple security features to authenticatea bank note. Cash receiving machines have less sophisticatedauthentication apparatus as they have to be kept to a relatively lowcost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 3 schematically illustrate components of known apparatus forimplementing different methods of observing birefringence;

FIG. 4 schematically illustrates a top-view of an authenticationapparatus in accordance with one or more embodiments of the presentinvention;

FIG. 5 schematically illustrates a side view of an authenticationapparatus in accordance with one or more embodiments of the presentinvention;

FIG. 6 schematically illustrates a circuit diagram for theauthentication apparatus in an illustrative embodiment;

FIG. 7 schematically illustrates the authentication apparatus in anoptional arrangement;

FIGS. 8a and 8b schematically illustrates the authentication apparatusin another optional arrangement;

FIG. 9a schematically illustrates a top view of the authenticationapparatus in a further optional arrangement;

FIG. 9b schematically illustrates a side view of the authenticationapparatus in a further optional arrangement;

FIG. 9c illustrates a graph of an output signal response ofbirefringence measuring apparatus of the authentication apparatus ofFIG. 9 a.

FIGS. 10a, 10b and 10c schematically illustrate detector arrangements ofthe reflectance measuring apparatus forming part of the authenticationapparatus according to one or more embodiments of the present invention;

FIG. 11 illustrates a graph plotting intensity of radiation received ata detector dependent upon an angle of incident radiation and an area ofthe detector;

FIG. 12 illustrates a graph plotting angle of incidence of illuminatingradiation versus reflectivity of the illuminating radiation from an itemsurface;

FIG. 13 illustrates a profile of intensity of reflected radiationreceived by a detector of a reflectance measuring apparatus when abanknote is passed through an authentication apparatus according to oneor more embodiments of the present invention;

FIG. 14 schematically illustrates a top view of an emitter-detector-itemarrangement of the reflectance measuring apparatus for use in anoptional arrangement of the authentication apparatus of one or moreembodiments of the present invention;

FIG. 15 schematically illustrates a top view of an emitter-detector-itemarrangement of the reflectance measuring apparatus for use in anoptional arrangement of the authentication apparatus of one or moreembodiments of the present invention; and

FIG. 16 schematically illustrates a perspective view of anemitter-detector-item arrangement of the reflectance measuring apparatusfor use in an optional arrangement of the authentication apparatus ofone or more embodiments of the present invention.

DETAILED DESCRIPTION

A variety of polymers may be used as secure substrates. Amongst these ispolypropylene film. The three main methods of manufacturingpolypropylene film are the stenter method, the cast method and thebubble method.

In the cast and stenter methods, polymer chips are typically placed inan extruder and heated so that an extrudate is forced out of a slit dieonto a chilled roller to form a film (in the case of the cast method) ora thick polymer ribbon (in the case of the stenter method). In thestenter method, the thick polymer ribbon is then reheated and thenstretched lengthways (termed the “machine direction”) and widthways(termed the “transverse direction”) to form a film.

In the bubble method, the polymer is extruded not through a slit die butthrough an annular die, to form a relatively thick extrudate, in theform of a hollow cylinder or “drainpipe” shape through which air isblown. The annular die is at the top of an apparatus which is typicallythe equivalent of several storeys high (for example 40 to 50 meters).The extrudate moves downwards and is heated sequentially so that it isexpanded to form a bubble. The bubble is then slit into twohalf-bubbles, each of which may be used individually as “monoweb” films;or alternatively the two halves may be nipped and laminated together toform a double thickness film (or the bubble may be collapsed to form adouble thickness film). Typically there are three concentric annuli atthe die, so that the hollow cylinder is an extrudate of three layers.For example, there may be a core layer of polypropylene with aterpolymer skin layer on one side and another terpolymer skin layer onthe other side. In this case the monoweb would consist of three layerswith polypropylene in the middle and the double web would consist offive layers because the layer in the middle would be the same skin layer(terpolymer) of each half-bubble. Many other possible arrangements andcomponents are possible, for example in terms of the number of annuli,type of skin layer, type of core layer, etc.

Thus the bubble method results in a thin film (for example 10 to 100microns thick) by forming a bubble whereas the stenter method results ina thin film by stretching the material. The bubble method results inhomogeneously stretched film which is different to and for some purposesadvantageous over stenter film Biaxially Oriented Polypropylene (BOPP)film is made by the bubble process by Innovia Films Ltd., Wigton, UK. Inaddition to polypropylene, other polymers (e.g. LLDPE,polypropylene/butylene copolymers) may also be formed as thin filmsusing the bubble process.

Previous authentication apparatus and methods make use of known sheetsof security document substrate which are permeable to electromagneticradiation, for example, transparent in the visible region of theelectromagnetic spectrum. It is known to create security documents, suchas banknotes, by printing opaque inks onto sheets of transparentplastics substrate material, leaving a transparent window. The resultingwindow provides an overt security feature which is conspicuous to thehuman eye. It is known to print, etch or embed additional opticalsecurity features, such as optically variable devices formed bydiffraction gratings, onto or into the resulting transparent windows, toprovide additional overt security features. It is known to provideautomatic authentication apparatus which can determine authenticity fromthe presence or absence of these additional optical security features,but such apparatus is typically complex and expensive.

WO 2009/133390 discloses a method of authenticating a polymer filmcomprising measuring the birefringence of a core layer therein.

Birefringence, or double refraction, is a property of materials causedby differences in the refractive indices of the material for the twodifferent polarisations, s- and p-, and between the two axes of itssurface place.

A birefringent material, when presented with polarised light, splits thelight into ordinary and extraordinary rays which are both retarded bytransmission through the birefringent material, but to differentdegrees. After transmission through a second polariser at 90° withrespect to the polarised light, the two rays recombine and interferewith one another destructively or constructively. The effect generatedis of variable transmission in the form of a sine wave as thebirefringent material is rotated from the minima (0° with respect to thepolarisers) to the maxima (45° with respect to the polarisers).

Birefringence is induced in transparent polymer films in three ways:crystal orientation, polymer chain orientation and crystal latticedeformation.

Refractive index is proportional to the density of a material; polymericmaterials exist in two forms, crystalline and amorphous, both of whichexist in a known proportion within a particular polymertype—polypropylene can be between 35% and 50% crystalline depending onits molecular weight range and its stereo-chemistry. During the bubbleprocess crystallisation occurs as the molten cast tube (1 mm thick) isquenched using chilled water; cooling is rapid and temperature gradientsoccur across the thickness of the film giving some directionality tocrystallisation. Crystalline areas form throughout the cast tubes thatare then pulled during the stretching process into their final shapewithin the finished polymer. Birefringence is caused by differences inthe lengths of the various dimensions of the crystalline regions andtheir orientation within the polymer; as the bubble polymer is stretchedequally in both machine and transverse directions, this is expected toaverage out producing a low birefringence; however uneven distributionof crystalline areas causes variance of birefringence over distances of1-3 mm.

Refractive index is also affected by the orientation of the polymerchains within the material; this has the largest effect on the overallbirefringence which is proportional to the ratio between the machinedirection and transverse direction stresses during stretching.

Finally, lattice deformation is theoretically a cause of birefringencebut is unlikely to be significant in a soft, low melting point materialsuch as polypropylene.

The resulting effect of the birefringence of a material manifests itselfas a rotation of the polarisation angle of light being transmittedthrough the material; the effect is initiated via an interfacialinteraction and propagated through the birefringent material; the degreeof birefringence observed is a product of the initial interfacialinteraction (i.e. the angle of incidence) and the subsequent path lengththrough the material.

As noted above, the birefringent effect is a product of the thickness ofthe film and the degree to which the refractive indices differ betweenthe two axes. The effect is visible if the film is placed between twocrossed polarisers and rotated through 90° between a minima (equivalentto no change in transmission from the crossed polarisers) to a maxima at45° where potentially as much light is transmitted as would be through asingle polariser.

Birefringence in films is induced by orientation differences inproduction between the machine and the transverse direction; theresulting films have two axes at 90° to one another at which points thebirefringence is at its minimum value, with 45° from either axis beingthe maximum. As a result of the nature of film processing in reels andsheets, every material produced by every known process will have thesame properties including the polarisers.

Because of the universality of the orientation of polymers, a singlemeasurement of birefringence at 45° is sufficient to determine themaximum value of any film and any printed product from that film. Thepolarisers themselves will also conform to this; therefore in themanufacture of a device such as this the specification for thepolarisers should be that they should be cut at 45° from a masterpolariser sheet.

The method and apparatus disclosed in WO 2009/133390 involves the use ofa pair of spinning polarisers that are at oriented at 90° to oneanother. The polarisers are operative to rotate at the same rate, andthe apparatus is operative to measure the intensity of the light thatpasses through a sample placed between the polarisers.

FIGS. 1 to 3 show components of apparatus for different methods ofobserving birefringence as disclosed in WO 2009/133390.

With reference to FIG. 1, a first method of observing birefringence isvia the use of crossed polarisers. Linear polarisers allow one type ofeither s- or p-polarised light to pass through them, so that when asecond linear polariser is presented and twisted 90° relative to thefirst, the remaining light made from a single polarised type is filteredout; this technique is referred to as using cross polarisers.Birefringent materials effectively rotate the axis of polarisation andso, when placed between two crossed polarisers will affect how muchlight is permitted to pass through them. Rotating the birefringentmaterial whilst between the crossed polarisers causes the intensity oflight to vary as the angles of birefringence alters. Thin polymer filmsoperate on the first order of birefringence and will tend to rotatelight between 0° and 90°; a fully birefringent material will vary fromno enhancement in transmission between the polarisers to eliminating theeffect of the first polariser by rotating light to pass through thesecond. This behaviour forms the basis of one method of measuring thebirefringence of the films; the sample is typically placed between twomotorised cross polarising filters which then rotate through 360° whilstmaintaining the same rotationary configuration with respect to oneanother, light passes from a source through the filter/sample/filter andits intensity is measured using a photodiode. The intensity measuredwill follow two 180° cycles the maximum and minimum values of which willbe related to the birefringence of that film.

With reference to FIG. 2, a second method for the measurement ofbirefringence is to use two circular-shaped linear polarising filtersthat are composed of sectors of material, each having its ownpolarisation angle which is related to the angular position of thesector on the circular optic. If two of these optics are differentiatedby their s- and p-orientations, then the combination of both will act ascross polarisers for each sector. A single light source can be used toilluminate a sample placed between two such polarisers and thetransmitted light from each sector can be fed into an optical fibrewhich in turn has the intensity transmitted measured using a photodiode.In this way, the birefringent behaviour of the film can be measured in asingle measurement without rotating the polarisers—the resolution ofsuch a measurement will depend on the angular size of each of thesectors—for example sectors as large as 20° would give eighteenmeasurements and would be more than sufficient for the finding of themaximal and the minimal transmissivities.

With reference to FIG. 3, a third method for the measurement of thebirefringence is the use of a quartz wedge. In this instance, thebirefringent material is placed between a polarising filter and acalibrated quartz wedge whilst light is shone through towards aninspection system that measures the positions of fringes on the wedge.

To differentiate between the designated genuine film and others, theabove-described birefringence measurement method may be employed toallow the user to eliminate other types of film, i.e. designatedcounterfeit films. BOPP film made by the stenter process is orientedmore in the transverse direction than the machine direction, and so isconsiderably more birefringent than BOPP films made by the double bubbleprocess. Birefringence can be controlled precisely using the doublebubble process and so can provide a unique signature that can eliminatefilms.

The method of WO 2009/133390 allows a film to be securitized as is. Theparticular inherent characteristics of the film are observed using thedisclosed method, and there is no need to add any further security oridentifying features. This identification allows authentication forsecurity purposes and also allows the film's origin to be determined.

The films referred to herein are generally sheet-form materials, and maybe provided as individual sheets, or as a web material which maysubsequently be processed (by die cutting for example) to provide sheetor article form materials. When referring to “film” in thisspecification it is intended, unless expressly provided otherwise, toinclude films in sheet, article or in web form.

The method of WO 2009/133390 is suitable for authenticating itemscontaining films made by the bubble process. The bubble process resultsin films which have balanced orientation, well-defined and uniformthicknesses and other properties (high tensile strength, low elongation,high gloss and clarity, good puncture and flex-crack resistance,resistance to oils and greases, good water-impermeability) which definea “signature” of the film which indicate that it has been prepared bythe bubble process.

In order to differentiate between films (e.g. BOPP films and others) theoverall thickness of the film, as well as the thickness of individuallayers, for example a laminating layer, may be measured. This allowsdetermination of particular characteristics which are dependent onparticular processes, for example a particular bubble process.Additionally, or alternatively, the unique birefringent signature of thefilm may be assessed and used to determine whether the film was made bya particular process and accordingly whether it is, for example, agenuine bank note or counterfeit. Birefringence depends on theanisotropy of the material and films made by bubble process havedifferent anisotropies and hence different birefringent properties tofilms made by other processes. Furthermore the precise conditions usedin the bubble process will affect the birefringent signature.

Thus WO 2009/133390 recognises that, rather than needing to add securityor identification features, the inherent properties of films made byparticular processes, such as the bubble process, are unique and act asa signature.

Actual counterfeit film is more likely to be bought rather than made bythe counterfeiter. There are several sources that can be broken intothree main groupings:

1. Cast or blown films—cast films are made by extruding polymer througha die onto a chilled roller. Blown films are made by extruding a polymerthrough a circular die and inflating a bubble in the semi-molten state.Cast films & blown films are typically either non or slightly orientedand so have inferior dimensional stability (i.e. they can easily bestretched), poorer optics and thickness control.

2. Mono oriented films—mono oriented films are made by extruding througha die and stretching in the machine direction. Mono oriented films arehighly oriented, they have poorer optics and poor transverse directiondimensional stability.

3. Biaxially oriented films—biaxially oriented films are commerciallyavailable from Innovia Films Limited and from a number of othersuppliers. Commercial grades of BOPP from many suppliers are generallymade by the stenter process where PP is extruded through a slot die ontoa chill roller, stretched in the machine direction over heated rollersand stretched in the transverse direction in a tenter frame. These filmsare anisotropic in nature unlike BOPP made by the double bubble process,which is stretch oriented evenly in all directions.

There exists the possibility that a counterfeiter may be aware of theabove-described birefringence effect. In order to deceive systemsemploying the above-described method, the counterfeiter may producecounterfeit items by printing on film at 45° to the film's sheet edge orreel edge. Whilst the difficulty of doing this may effectively rule outany industrial process, the danger might remain for a knowledgeable anddetermined counterfeiter.

The above described birefringence measurement methods may require arelatively lengthy amount of time to make appropriate measurements. Inpractice this may be greater than one second, thereby effectively rulingout high speed measurements. Also, there is the issue of item placementand measurement area. Transparent or “window” regions of items may besmall and partially covered with print. Thus, in the particular field ofbanknote authentication, an automatic alignment to a particulardenomination may be possible, but this might become awkward in manualuse. This is further complicated by the size of the measurement area:large areas can be more accurate but will be more likely to accidentallyincorporate some of the printed areas of the window.

The above described birefringence measuring method may be useful forauthenticating films which form part of security documents. However, insome instances, those security documents may comprise film substrateswhere at least a portion of the film substrate is printed upon. Toensure that a correct birefringence measurement for the film substrateitself is taken, the measurement should be made on the unprinted or“window” region of the film, i.e. an item authentication region of theitem. A birefringence measurement performed on a printed area of thefilm substrate may result in a “false positive”, because thebirefringence measurement reading for the printed region may be of asimilar level to that of a genuine film. Therefore, it is important thatthat the birefringence measurement is performed on the unprinted or“window” region (i.e. directly on the film substrate) of the item ratherthan on a printed region to avoid such “false positives” and to obtainan accurate birefringence measurement of the film substrate. Anon-window area could be mistaken for an area of low birefringence orair when placed between two polarisers, because in both situationstransmission is low between the crossed-polarisers.

As may be appreciated, the need to ensure that it is the window region(or item authentication region) of the item upon which birefringencemeasurement is performed, rather than on a printed region, may requiresome manipulation of the item on the part of a user. The user may needto move the item within the measuring apparatus until the window regionof the item is located in a measuring region where the birefringencemeasurement method can be performed. This may prove time consumingwhilst the user manipulates the item to properly locate the window inthe measuring region.

It may be desirable to implement a birefringence measurement method forthe authentication of items using machine feeding apparatus. This maypotentially increase the speed at which items can be authenticated.

The present invention has been devised with the foregoing considerationsin mind.

According to an aspect of the present invention, there is provided anauthentication apparatus operative to determine the authenticity of anitem comprising a film substrate responsive to detection that a portionof the item located in a measuring region of the apparatus has apredetermined birefringence characteristic, the apparatus comprising: anitem detection arrangement operative to determine if at least a portionof an item is located in a measuring region of the authenticationapparatus; and an optically-based birefringence measuring apparatus,wherein the authentication apparatus is operative to compare a measuredbirefringence characteristic with a predetermined birefringencecharacteristic and to produce an authenticity signal indicative ofauthenticity or otherwise of the item based upon the comparison, theapparatus further comprising a control means operative to control outputof the authenticity signal from the apparatus responsive todetermination, by the item detection arrangement, of presence orotherwise of the at least a portion of the item in the measuring region.

This may allow the apparatus to output an authenticity signal only whena portion of an authentic or genuine item is located in the measuringregion. The operation of the item detector arrangement may serve toreduce power consumption of the apparatus: the authenticity signal maybe output by the apparatus only when an item is present. Otherwise, nosignal is output.

Optionally, the item detection arrangement may comprise an itemdetection emitter located, and operative, to illuminate withelectromagnetic radiation an item detection region of the apparatus, andan item detection detector, located, and operative, to receive at leastone of: electromagnetic radiation reflected from the item detectionregion; and electromagnetic radiation transmitted through the itemdetection region, wherein the item detection detector is furtheroperative to provide a signal indicative of presence or otherwise of anitem in the item detection region, and further wherein the itemdetection arrangement is operative to determine that the at least aportion of the item is located in the measuring region responsive toreceipt of the item detection detector signal indicating presence of anitem in the item detection region.

The item detection emitter may be operative to emit white-light and/orinfra-red light, and the item detection detector may be operative todetect white-light and/or infra-red light.

Further optionally, the apparatus may be operative to differentiatebetween item film substrates made by a bubble process and item filmsubstrates made by a different process.

The optically-based birefringence measuring apparatus may comprise abirefringence measurement emitter located, and operative, to illuminatethe measuring region of the apparatus with electromagnetic radiation; afirst polariser located between the birefringence measurement emitterand a first side of the measuring region so that electromagneticradiation emitted by the birefringence measurement emitter passestherethrough; a birefringence measurement detector located on a secondside of the measuring region, and operative to receive electromagneticradiation transmitted through the measuring region from thebirefringence measurement emitter; and a second polariser locatedbetween the second side of the measuring region and the birefringencemeasurement detector so that electromagnetic radiation transmittedthrough the measuring region passes therethrough, the second polariseroriented so as to effect polarisation in a direction transverse to thatof the first polariser; wherein the birefringence measurement detectoris operative to output a signal corresponding to a measuredbirefringence characteristic.

The output signal output by the birefringence measurement detectorcorresponding to a measured birefringence characteristic may beproportional to an intensity of transmitted electromagnetic radiationreceived.

Optionally, the birefringence measurement detector may be operative tocommunicate the output signal corresponding to a measured birefringencecharacteristic to a processor which is operative to compare a value ofthe output signal with the predetermined birefringence characteristic.

Further optionally, the predetermined birefringence characteristic maycomprise one of: a first range of values corresponding to expectedbirefringence measurement detector output signal values if an opaque orsemi-opaque region of the item is located in the measuring region; asecond range of values corresponding to expected birefringencemeasurement detector output signal values if a transparent orsemi-transparent region of the item is located in the measuring region;and a third range of values corresponding to expected birefringencemeasurement detector output signal values if no item is present in themeasuring region.

The birefringence measurement emitter may comprise a light source.Optionally, the light source may comprise a white light emitting LED.

The birefringence measurement detector may comprise a photodetector.Optionally, the photodetector may comprise a photodiode. Furtheroptionally, the photodiode may be suitable for detecting white light.

The birefringence measurement emitter may be slidably mounted on a railor rod. Optionally, the birefringence measurement emitter may beattached to the rail or rod by an attachment which is slidable relativeto the rail or rod, and which attachment may comprise a fixing element(e.g. a locking screw) to allow a position of the birefringencemeasurement emitter to be fixed relative to the rail or rod.

The birefringence measurement detector may be slidably mounted on a railor rod. Optionally, the birefringence measurement detector may beattached to the rail or rod by an attachment which is slidable relativeto the rail or rod, and which attachment may comprise a fixing element(e.g. a locking screw) to allow a position of the birefringencemeasurement detector to be fixed relative to the rail or rod.

Optionally, the item detection arrangement may comprise anoptically-based reflectance measuring apparatus for determining if anitem authentication region is located in the measuring region, whereinthe reflectance measuring apparatus may comprise: a reflectancemeasurement emitter operative to illuminate the measuring region of theapparatus with electromagnetic radiation; and a reflectance measurementdetector located and operative to receive electromagnetic radiationreflected from the measuring region of the apparatus and operative tooutput a signal corresponding to a measured characteristic of theelectromagnetic radiation reflected from the measuring region andindicative of presence or otherwise of an item authentication region inthe measuring region, wherein the reflectance measuring apparatus isoperative to compare a measured reflection characteristic with a set ofpredetermined reflection characteristics and to determine presence orotherwise of the item authentication region in the measuring regionbased upon the comparison, and further operative to provide to thecontrol means a signal indicative of the determination for controllingoutput of the authenticity signal from the control means.

This may allow the apparatus to output an authenticity signal only whenan item authentication region of an item is located in the measuringregion. At all other times, another signal type may be output by theapparatus. For example, the signal may comprise a signal indicating thatno sample is present or, for example, a signal indicating that theregion of the item which is located in the measuring region is not theauthentication region (e.g. a non-window region or printed region of theitem)).

Optionally, the output signal output by the reflectance measurementdetector corresponding to a measured reflection characteristic may beproportional to an intensity of reflected electromagnetic radiationreceived.

Optionally, the reflectance measurement detector may be operative tocommunicate the output signal corresponding to a measured reflectioncharacteristic to a processor which is operative to compare a value ofthe output signal corresponding to the measured reflectioncharacteristic with the predetermined reflection characteristic, whichmay comprise a pre-defined value indicative of presence of an itemauthentication region of the item in the measuring region, and theprocessor operative to implement the determination that the itemauthentic region is present or absent in the measuring region based uponthe comparison and operative to provide to the control means the signalindicative of the determination.

Optionally, if the comparison of the predetermined reflectioncharacteristic with the output signal output by the reflectancemeasurement detector corresponding to a measured reflectioncharacteristic indicates that the item authentication region is locatedin the measuring region, the processor is operative to output adetermination signal to the control means indicative of presence of theitem authentication region in the measuring region, wherein responsiveto receipt thereof, the control means is operative to output theauthenticity signal indicative of authenticity or otherwise of the itembased upon the comparison of the predetermined birefringencecharacteristic with the output signal output by the birefringencemeasurement detector corresponding to a measured birefringencecharacteristic.

Optionally, the predetermined reflection characteristic may comprise oneor more of: a first range of values corresponding to expectedreflectance measurement detector output signal values if an opaque orsemi-opaque region of the item is located in the measuring region; asecond range of values corresponding to expected reflectance measurementdetector output signal values if a transparent or semi-transparentregion of the item is located in the measuring region; and a third rangeof values corresponding to expected reflectance measurement detectoroutput signal values if no item is present in the measuring region.

Optionally, the reflectance measurement detector may have associatedtherewith a shade, the shade including at least one aperture, whereinthe aperture may be located with respect to the reflectance measurementdetector to permit electromagnetic radiation reflected from the at leasta portion of the item to be received by the reflectance measurementdetector.

Optionally, the shade may comprise a tube, and in which the aperture maycomprise the hollow portion of the tube. Further optionally, theaperture may comprise a tubular region in the shade. The reflectancemeasurement detector may be located at an end of the tube, or within thetube, or at an end of, or within, the tubular region of the shade.

Optionally, the reflectance measurement emitter has associated therewitha shade, the shade including an aperture, wherein the aperture islocated with respect to the reflectance measurement emitter to permitelectromagnetic radiation emitted from the reflectance measurement demitter to be directed toward the measuring region of the apparatus.

Optionally, the shade may comprise a tube, and in which the aperture maycomprise the hollow portion of the tube. Further optionally, theaperture may comprise a tubular region in the shade. The reflectancemeasurement emitter may be located at an end of the tube, or within thetube, or at an end of, or within, the tubular region of the shade.

Optionally, the reflectance measurement emitter is operative to emitcoherent electromagnetic radiation. Further optionally, the reflectancemeasurement emitter may comprise at least one LED. The at least one LEDmay be operative to emit light in the infra-red range of theelectromagnetic spectrum and/or may comprise a white light emittersource. Yet further optionally, the reflectance measurement emitter maycomprise at least one strip electromagnetic radiation source.

Optionally, the reflectance measurement detector may comprise at leastone photodiode. Further optionally, the at least one photodiode may beoperative to detect light in the infra-red range of the electromagneticspectrum. Yet further optionally, the reflectance measurement detectormay comprise at least one line-scan camera and/or may comprise at leastone spectrometer and a CCD or CMOS image sensor.

Optionally, the reflectance measurement emitter may comprise at leastone of: a plurality of LEDs; a plurality of white light emitter sources;and a plurality of strip electromagnetic radiation sources; and thereflectance measurement detector may comprise at least one of: aplurality of photodiodes; a plurality of line-scan cameras; and aplurality of spectrometers and CCD or CMOS image sensors; wherein eachone of the plurality of LEDs is paired with a corresponding one of theplurality of photodiodes and/or plurality of line-scan cameras and/orplurality of spectrometers and CCD or CMOS image sensors, wherein eachone of the plurality of white light emitter sources may be paired with acorresponding one of the plurality of photodiodes and/or plurality ofline-scan cameras and/or plurality of spectrometers and CCD or CMOSimage sensors, and wherein each one of the plurality of stripelectromagnetic radiation sources may be paired with a corresponding oneof the plurality of photodiodes and/or plurality of line-scan camerasand/or plurality of spectrometers and CCD or CMOS image sensors.

Optionally, at least one of the plurality of LEDs may be operative toemit light in the infra-red range of the electromagnetic spectrum.Further optionally, at least one of the plurality of photodiodes may beoperative to detect light in the infra-red range of the electromagneticspectrum.

The apparatus optionally may include a transport path, of which a partmay comprise the measuring region, and along which item transport paththe item may be conveyable.

The item may comprise a banknote.

The opaque or semi-opaque region may comprise a printed region of thebanknote and/or the transparent or semi-transparent region of the itemmay comprise an unprinted or window region (item authentication region)of the banknote.

According to another aspect of the present invention, there is provideda banknote counting apparatus comprising the authentication apparatuswhich includes any one or more of the above-described features, thebanknote counting apparatus further comprising a note counting deviceoperative to maintain a count of banknotes conveyed through theapparatus, and the note counting device further operative to receive theauthenticity signal indicative of authenticity or otherwise of the itemfrom the authentication apparatus, wherein the note counting device isoperative to alter a note count only when the signal indicates that anitem in the measuring region is authentic.

Optionally, upon receipt of the signal indicating that the item in themeasuring region is authentic, the note counting device may be operativeto alter the note count. Further optionally, the note counting devicemay be operative to alter the note count by incrementing the count.

According to another aspect of the present invention, there is provideda method of authenticating an item comprising a film substrate, themethod comprising detecting if a portion of an item located in ameasuring region of an authentication apparatus has a predeterminedbirefringence characteristic, and further comprising the steps of:determining, by an item detection arrangement, if at least a portion ofan item is located in a measuring region of the authenticationapparatus; comparing a measured birefringence characteristic, obtainedby an optically-based birefringence measuring apparatus, with apredetermined birefringence characteristic; producing an authenticitysignal indicative of authenticity or otherwise of the item based uponthe comparison; controlling, by way of a control means, output of theauthenticity signal from the apparatus responsive to determination, bythe item detection arrangement, of presence or otherwise of the at leasta portion of the item in the measuring region.

Optionally, the method may comprise illuminating with electromagneticradiation, by way of an item detection emitter forming part of the itemdetection arrangement, an item detection region of the apparatus, andreceiving, by way of an item detection detector forming part of the itemdetection arrangement, at least one of: electromagnetic radiationreflected from the item detection region; and electromagnetic radiationtransmitted through the item detection region, and further comprisingproviding a signal indicative of presence or otherwise of an item in theitem detection region and, responsive to receipt of an item detectiondetector signal indicating presence of an item in the item detectionregion, determining, by the item detector arrangement, that the at leasta portion of the item is located in the measuring region.

Optionally, the method may differentiate between item film substratesmade by a bubble process and item film substrates made by a differentprocess.

Optionally, the method may comprise illuminating, with a birefringencemeasurement emitter, the measuring region of the apparatus withelectromagnetic radiation; locating a first polariser between thebirefringence measurement emitter and a first side of the measuringregion so that electromagnetic radiation emitted by the birefringencemeasurement emitter passes therethrough; locating a birefringencemeasurement detector on a second side of the measuring region;receiving, at the birefringence measurement detector, electromagneticradiation transmitted through the measuring region from thebirefringence measurement emitter; locating a second polariser betweenthe second side of the measuring region and the birefringencemeasurement detector so that electromagnetic radiation transmittedthrough the measuring region passes therethrough; orienting the secondpolariser so as to effect polarisation in a direction transverse to thatof the first polariser; outputting, from the birefringence measurementdetector, a signal corresponding to a measured birefringencecharacteristic.

Optionally, the method may comprise communicating the output signalcorresponding to a measured birefringence characteristic to a processor;and comparing, in the processor, a value of the output signal with thepredetermined birefringence characteristic.

Optionally, the predetermined birefringence characteristic may compriseone of: a first range of values corresponding to expected birefringencemeasurement detector output signal values if an opaque or semi-opaqueregion of the item is located in the measuring region; a second range ofvalues corresponding to expected birefringence measurement detectoroutput signal values if a transparent or semi-transparent region of theitem is located in the measuring region; and a third range of valuescorresponding to expected birefringence measurement detector outputsignal values if no item is present in the measuring region.

Optionally, the method may comprise: determining, by way on anoptically-based reflectance measuring apparatus of the item detectionarrangement, if an item authentication region of an item is located inthe measuring region, the determining step implemented by: illuminating,by way of a reflectance measurement emitter of the reflectance measuringapparatus, the measuring region of the apparatus with electromagneticradiation; receiving, by way of a reflectance measurement detector ofthe reflectance measuring apparatus, electromagnetic radiation reflectedfrom the measuring region of the apparatus; outputting, from thereflectance measurement detector, a signal corresponding to a measuredcharacteristic of the electromagnetic radiation reflected from themeasuring region and indicative of presence or otherwise of an itemauthentication region in the measuring region; comparing, in thereflectance measuring apparatus, a measured reflection characteristicwith a set of predetermined reflection characteristics; and determiningpresence or otherwise of the item authentication region in the measuringregion based upon the comparison; and providing, to the control means, asignal indicative of the determination for controlling output of theauthenticity signal from the control means.

Optionally, the method may comprise communicating the output signalcorresponding to a measured reflection characteristic to a processorwhich is operative to compare a value of the output signal correspondingto the measured reflection characteristic with the predeterminedreflection characteristic, which may comprise a pre-defined valueindicative of presence of an item authentication region of the item inthe measuring region, and the processor operative to implement thedetermination that the item authentication region is present or absentin the measuring region based upon the comparison and operative toprovide to the control means the signal indicative of the determination.

Optionally, if the comparison of the predetermined reflectioncharacteristic with the output signal output by the reflectancemeasurement detector corresponding to a measured reflectioncharacteristic indicates that the item authentication region is locatedin the measuring region, outputting, from the processor to the controlmeans, a determination signal indicative of presence of the itemauthentication region in the measuring region, wherein responsive toreceipt thereof, outputting, from the control means, the authenticitysignal indicative of authenticity or otherwise of the item based uponthe comparison of the predetermined birefringence characteristic withthe output signal output by the birefringence measurement detectorcorresponding to a measured birefringence characteristic.

The predetermined reflection characteristic may comprise one or more of:a first range of values corresponding to expected reflectancemeasurement detector output signal values if an opaque or semi-opaqueregion of the item is located in the measuring region; a second range ofvalues corresponding to expected reflectance measurement detector outputsignal values if a transparent or semi-transparent region of the item islocated in the measuring region; and a third range of valuescorresponding to expected reflectance measurement detector output signalvalues if no item is present in the measuring region.

The opaque or semi-opaque region may comprise a printed region of abanknote and/or the transparent or semi-transparent region of the itemmay comprise an unprinted or window region (item authentication region)of the banknote.

Optionally, the method may comprise providing a transport path in theauthentication apparatus, of which a part of the transport path maycomprise the measuring region, and conveying the item along thetransport path.

According to another aspect of the present invention, there is provideda banknote counting method comprising any one or more of the methodsteps described above, the banknote counting method further comprisingmaintaining, using a note counting device, a count of banknotes conveyedthrough the apparatus; receiving, at the note counting device, from theauthentication apparatus, the authenticity signal indicative ofauthenticity or otherwise of the item; and altering a note count onlywhen the authenticity signal indicates that an item in the measuringregion is authentic.

Optionally, the method may further comprise altering the note count uponreceipt of an authenticity signal indicating that an item in themeasuring region is authentic. Further optionally, the method maycomprise altering the note count by incrementing the count.

One or more specific embodiments in accordance with aspects of thepresent invention will be described, by way of example only, and withreference to the following drawings.

FIGS. 1 to 3 schematically illustrate components of known apparatus forimplementing different methods of observing birefringence;

FIG. 4 schematically illustrates a top-view of an authenticationapparatus in accordance with one or more embodiments of the presentinvention;

FIG. 5 schematically illustrates a side view of an authenticationapparatus in accordance with one or more embodiments of the presentinvention;

FIG. 6 schematically illustrates a circuit diagram for theauthentication apparatus in an illustrative embodiment;

FIG. 7 schematically illustrates the authentication apparatus in anoptional arrangement;

FIGS. 8a and 8b schematically illustrates the authentication apparatusin another optional arrangement;

FIG. 9a schematically illustrates a top view of the authenticationapparatus in a further optional arrangement;

FIG. 9b schematically illustrates a side view of the authenticationapparatus in a further optional arrangement;

FIG. 9c illustrates a graph of an output signal response ofbirefringence measuring apparatus of the authentication apparatus ofFIG. 9 a.

FIGS. 10a, 10b and 10c schematically illustrate detector arrangements ofthe reflectance measuring apparatus forming part of the authenticationapparatus according to one or more embodiments of the present invention;

FIG. 11 illustrates a graph plotting intensity of radiation received ata detector dependent upon an angle of incident radiation and an area ofthe detector;

FIG. 12 illustrates a graph plotting angle of incidence of illuminatingradiation versus reflectivity of the illuminating radiation from an itemsurface;

FIG. 13 illustrates a profile of intensity of reflected radiationreceived by a detector of a reflectance measuring apparatus when abanknote is passed through an authentication apparatus according to oneor more embodiments of the present invention;

FIG. 14 schematically illustrates a top view of an emitter-detector-itemarrangement of the reflectance measuring apparatus for use in anoptional arrangement of the authentication apparatus of one or moreembodiments of the present invention;

FIG. 15 schematically illustrates a top view of an emitter-detector-itemarrangement of the reflectance measuring apparatus for use in anoptional arrangement of the authentication apparatus of one or moreembodiments of the present invention; and

FIG. 16 schematically illustrates a perspective view of anemitter-detector-item arrangement of the reflectance measuring apparatusfor use in an optional arrangement of the authentication apparatus ofone or more embodiments of the present invention.

FIGS. 4 and 5 illustrate an authentication apparatus 100 which comprisesa birefringence measuring apparatus 102 and a reflectance measuringapparatus 104.

The authentication apparatus 100 is operative to measure birefringenceand reflectance characteristics of an item 106 (e.g. a banknote). Inparticular, the authentication apparatus 100 is operative to measurebirefringence and reflectance characteristics of a portion of the item106 located in a measuring region 108 of the authentication apparatus100.

The birefringence measuring apparatus 102 comprises a first emitter 110,or birefringence measurement emitter (optionally an LED operative toemit white-light), a first polariser 112, a first detector 114, orbirefringence measurement detector (optionally a photodiode operative todetect white light), and a second polariser 116.

The elements of the birefringence measuring apparatus 102 are arrangedsuch that the first emitter 110 and first polariser 112 are located on afirst side of the measuring region 108, and the first detector 114 andthe second polariser 116 are located on a second side of the measuringregion 110 (i.e. opposite the first emitter 110 and first polariser112).

First emitter 110 is operative to illuminate the measuring region 108with electromagnetic radiation (denoted by dotted arrow IL in thefigure), and first detector 114 is oriented and operative to receiveelectromagnetic radiation (denoted by dotted arrow TL in the figure)which is transmitted through a portion of the item 106 located in themeasuring region 108. The illuminating electromagnetic radiation IL1passes through first polariser 112 prior to irradiating a portion of theitem 106 located in the measuring region 108. After passing through theportion of the item 106 located in the measuring region 108, thetransmitted electromagnetic radiation TL passes through second polariser116 before being received by first detector 114.

In the illustrated arrangement, the measuring region 108 is located in afirst plane. The first polariser 112 is spaced from the first plane andis located in a second plane on a first side of the measuring region108. The second plane is substantially parallel to the first plane.Similarly, the second polariser 116 is spaced from the first plane andis located in a third plane on a second side of the measuring region108. It is located opposite the first polariser 112, and the third planeis substantially parallel to the first and second planes. Thearrangement of transmission orientations of the first and secondpolarisers 112, 116 is such that they comprise crossed polarisers. Thatis, the first polariser 112 is arranged such that a transmissionorientation thereof is about +45° to a transmission orientation of theportion of the item 106 located in the measuring region 108. The secondpolariser 116 is arranged such that a transmission orientation thereofis about −45° to the transmission orientation of the portion of the item106 located in the measuring region 108. Alternatively, the transmissionorientation of the first polariser 112 may be such that it is about −45°to a transmission orientation of the portion of the item 106 located inthe measuring region 108 and the transmission orientation of the secondpolariser 116 may be such that it is about +45° to the transmissionorientation of the portion of the item 106 located in the measuringregion 108.

Thus, in the illustrated arrangement, the illuminating electromagneticradiation IL1 emitted by first emitter 110 will be polarised by thefirst polariser 112, irradiate the portion of the item 106 located inthe measuring region 108, pass through the item 106, continue astransmitted electromagnetic radiation TL to the second polariser 116(i.e. crossed polariser) and pass therethrough, and continue forreception by the first detector 114. The first detector 114 responsiveto detection of transmitted electromagnetic radiation TL incidentthereon, outputs a signal proportional to the intensity of receivedtransmitted electromagnetic radiation TL to a processing means (notshown).

The processing means, upon receiving an output signal from the firstdetector 114, is operative to compare a value of the received signalwith a set of pre-defined values stored in a database (not shown). Thesepre-defined values may correspond to expected transmittedelectromagnetic radiation values when one or more of: a printed regionof an item is located in the measuring region 108; an unprinted regionof an item (e.g. a window region or item authentication region) islocated in the measuring region 108 (where the film substrate of theitem is genuine); an unprinted region of an item (e.g. a window region)is located in the measuring region 108 (where the film substrate of theitem is not genuine); and no banknote is located in the measuring region108.

The first emitter 110 is slidably mounted on a rail or rod 118. Thefirst emitter 110 may be fixed at a particular position along a lengthof said rail or rod 118 by way of fixing screw 120. This arrangementallows the position of the first emitter 110 relative to the measuringregion 108 to be altered. Similarly, first detector 114 is slidablymounted on a rail or rod 122. The first detector 114 may be fixed at aparticular position along a length of said rail or rod 122 by way offixing screw 124. Again, this arrangement allows the position of thefirst detector 114 relative to the measuring region 108 to be altered.

An item 106 comprising a film that is highly oriented will give rise toa high reading from the first detector 114 (because a large amount ofelectromagnetic radiation will be transmitted, i.e. the intensity of thetransmitted electromagnetic radiation TL will be relatively high).However, a balanced film will give rise to a zero-value or low readingfrom the first detector 114 because the behaviour of the electromagneticradiation through the first and second crossed polarisers will belargely unaltered.

Films having a balanced orientation (e.g. BOPP films) will produce a lowbirefringence signal at the first detector 114. Such a signal may besubstantially the same as that corresponding to a printed area of filmor no film at all in the measuring region 108. On the other hand, when astenter or other oriented film is located in the measuring region 108,the first detector 114 will produce a high birefringence signal thatwill be different from all the above situations.

The birefringence measuring apparatus 102 is therefore capable ofoperating on the basis of a “item is authentic” result all the timeuntil an item comprising a false piece of film is encountered, at whichpoint an alarm and/or visual alert may be activated: in other words itwill find a negative but not identify a positive.

To counter this, the authentication apparatus 100 includes thereflectance measuring apparatus 104.

The reflectance measuring apparatus 104 comprises a second emitter 126,or reflectance measurement emitter (optionally an LED operative to emitelectromagnetic radiation in the infra-red region of the electromagneticspectrum), a second detector 128, or reflectance measurement detector(optionally a photodiode operative to detect electromagnetic radiationin the infra-red region of the electromagnetic spectrum), and a shade130 associated with the second detector 128. The shade 130 serves toprotect the second detector 128 from stray light so as to prevent falsereadings caused by stray light being incident upon the second detector128 from sources other than the second emitter 126.

The reflectance measuring apparatus 104 is configured such that thesecond emitter 126 and second detector 128 are oriented to face themeasuring region 108. Second emitter 126 is operative to illuminate themeasuring region 108 with electromagnetic radiation (denoted by arrowIL2 in the figure), and second detector 128 is oriented and operative toreceive electromagnetic radiation (denoted by arrow RL in the figure)reflected from the portion of the item 106 located in the measuringregion 108.

In an optional arrangement, the authentication apparatus 100 maycomprise a path along which an item may be conveyed. The measuringregion 108 forms part of this path. Thus, in this particulararrangement, the item may be conveyed along the path from one side ofthe authentication apparatus 100 to the other and, during its transit,pass through the measuring region 108. That is, in this optionalarrangement, the item to be authenticated may be moved relative to theauthentication apparatus 100 or vice versa. Such an optional arrangementwill be described in more detail in relation to FIG. 7. In anotheroptional arrangement, authentication measurement may take place when anitem is static. That is, the item may be introduced to an item locationregion (of which the measuring region 108 forms part) of theauthentication apparatus 100, where the item is held until anauthentication measurement has taken place. Such an optional arrangementwill be described in more detail in relation to FIGS. 8a and 8 b.

In operation, the item 106 is introduced into the authenticationapparatus 100 such that a portion of the item 106 will be located in themeasuring region 108. At that time, illuminating electromagneticradiation IL2 from second emitter 126 is incident upon the portion ofthe item 106 located in the measuring region 108. At least a portion ofthe illuminating electromagnetic radiation IL2 incident upon the item106 in the measuring region 108 will be reflected by the portion of theitem 106 in the measuring region 108. This reflected electromagneticradiation RL is reflected toward second detector 128. As it nears thesecond detector 128, it will pass through an aperture of shade 130 andis then detected by second detector 128. The second detector 128,responsive to detection of reflected electromagnetic radiation RLincident thereon, outputs a signal proportional to the intensity ofreceived reflected electromagnetic radiation RL to the processing means(not shown).

The processing means, upon receiving an output signal from the seconddetector 128, is operative to compare a value of the received signalwith a set of pre-defined values stored in a database (not shown). Thesepre-defined values may correspond to expected reflected electromagneticradiation values when one or more of: a printed region of an item islocated in the measuring region 108; an unprinted region of an item(e.g. a window region) is located in the measuring region 108 (where thefilm substrate of the item is genuine); an unprinted region of an item(e.g. a window region) is located in the measuring region 108 (where thefilm substrate of the item is not genuine); and no banknote is locatedin the measuring region 108.

The processing means may be arranged to transmit an output signal to oneor more visual or audio alert systems based upon output signals receivedfrom said first detector 114 and second detector 128.

Therefore, in an optional arrangement, if no item is present in themeasuring region 108, the processing means may issue an output signal tocontrol a visual alert system to display a first visual alert (e.g. ared light) and an audio alert system to output a first audio alert (e.g.a buzzer). If a printed region of an item is present in the measuringregion 108, the processing means may issue an output signal to control avisual alert system to display a first visual alert (e.g. a red light)and an audio alert system to output a first audio alert (e.g. a buzzer).If a window region of an item is present in the measuring region 108 andwhere the film substrate forming the item is genuine (as determined bythe birefringence measuring apparatus), the processing means may issuean output signal to control a visual alert system to display a secondvisual alert (e.g. a green light) and an audio alert system to besilent. If a window region of an item is present in the measuring region108 and where the film substrate forming the item is non-genuine (asdetermined by the birefringence measuring apparatus), the processingmeans may issue an output signal to control a visual alert system todisplay a first visual alert (e.g. a red light) and an audio alertsystem to output a first audio alert (e.g. a buzzer).

This apparatus 100 may be implemented in, for example, a banknotecounting system. The processing means may be operative to output asignal to a counting device only when the signals received from thebirefringence measuring apparatus 102 and the reflectance measuringapparatus 104 are indicative that a window region of the item 106 islocated in the measuring region 108, and that the film substrate formingthe window region is authentic. However, no signal may be output whenthe signals received from the birefringence measuring apparatus 102 andthe reflectance measuring apparatus 104 are indicative that a windowregion of the item 106 is located in the measuring region 108, but thatthe film substrate forming the window region is not authentic. That is,a count made by the counting device may be altered only when a genuinewindow region is registered in the measuring region 108.

In the illustrated arrangement of FIGS. 4 and 5, the first emitter 110comprises a light emitting diode (LED) which is operative to emit whitelight and the first detector 114 comprises a photodiode operative todetect white light.

Further, the second emitter 126 comprises an LED which is operative toemit electromagnetic radiation at wavelengths corresponding to theinfra-red (IR) region of the electromagnetic spectrum. Optionally, theLED is operative to emit electromagnetic radiation with wavelengthsabout 890 nm.

The second detector 128 in the illustrated arrangement comprises aphotodiode operative to detect electromagnetic radiation at wavelengthscorresponding to the IR region of the electromagnetic spectrum and,optionally, to detect electromagnetic radiation with wavelengths betweenabout 880 nm and 1140 nm.

Of course, in further optional arrangements, the second emitter 126 andsecond detector 128 may be operative to emit and detect electromagneticradiation at other wavelengths in the electromagnetic spectrum.

In the arrangement where the LED of the second emitter 126 is operativeto emit electromagnetic radiation having wavelengths of about 890 nm,the photodiode of the second detector 128 is operative to generate avoltage of approximately 350 mV max upon the detection of light between880 nm and 1140 nm.

The sensitivity of reflectance measuring apparatus 104 is dependent uponthe angle of the second emitter 126 and second detector 128 to oneanother, the distance and angle of the measuring region 108 relative tothe second emitter 126 and second detector 128, the levels of ambientlight and the size of the shade 130.

The shade 130 in the illustrated arrangement comprises a tubular element(optionally a black tube). The second detector 128 may be located at, ornear, one end of the tubular element on a first side of the shade 130(or (or within the tubular element near a first side of the shade 130).The tubular element is located and oriented relative to the secondemitter 126 and measuring region 108 such that reflected electromagneticradiation RL reflected from the measuring region 108 enters the tubularelement at a mouth portion thereof. After entering the tubular elementvia mouth portion, the reflected electromagnetic radiation RL travelsalong tubular element to the second detector 128. The length anddiameter of the tube determine the angle range of incidentelectromagnetic radiation that is admitted to the second detector 128(i.e. the longer and narrower the tube is, the narrower the angle rangeof incident electromagnetic radiation that is admitted). An arrangementsuch as this can differentiate between a polymer window, a printedsurface and air due to differences in the gloss of each of thesematerials.

With the gloss measurement (i.e. the measurement performed by thereflectance measuring apparatus 104) in place, the authenticationapparatus 100 now has the information that the birefringence is eitherlow or high and that there is the presence or absence of a window.Optionally, the reflective gloss system is positioned on the oppositeside of the polarisation system from the first emitter 110, to reduce orinhibit the impact of light leakage from the first emitter 110 into theinfra-red detector (light is only permitted through the films when thereis a highly birefringent film between them, at this point light leakageinto the infra-red detector is unimportant because there will actuallybe a window present).

The width of the spacing between the reflectance measuring apparatus 104and the item to be authenticated will affect the accuracy of the windowpresence detection system (i.e. reflectance measuring apparatus 104).There may be a trade-off between the minimum practical width of the itemslit, to ensure the flattest possible reading and the range of anglesaccepted by the second detector (the wider the range accepted, thegreater the danger of false signals).

An issue of consequence for component placement is the vertical positionand size of the first emitter, 110, first detector 114, second emitter126 and second detector 128. Item windows (e.g. banknote windows) arenot always in the same place vertically and, whilst a swiping system(e.g. as illustrated in FIG. 7) would take into account the horizontalplacement of the window, the vertical placement of the window in theitem would need to be taken into account also. To counter this, in anoptional arrangement, two or more positions of the item surface could bemeasured and/or the emitters and detectors could be movable. As isillustrated in FIGS. 4 and 5, the emitters and detectors are mounted onrails 118, 122. To allow flexibility of the authentication apparatus 100where it is to be used to authenticate items such as, for example,banknotes (where the window region locations in notes may be differentfor different denominations or where window region locations in notesmay be different for different countries), the rail system could allowan initial adjustment to be made to the specified height, and then theemitters and detectors could be fixed at that height.

Optionally, multiple emitters and detectors may be mounted on the samerail and/or longer detector arrays and emitter sources could beemployed.

FIG. 6 is a schematic circuit diagram for the authentication apparatus100. Features such as, for example, capacitors, resistors, etc. areomitted to aid clarity.

The circuit comprises a power source 131 which is operative to power thefirst emitter 110, second emitter 126 and processor 132.

First detector 114 and second detector 128 are coupled to the processor132 (optionally a microcontroller) so that output signals output bythese devices are received by the processor 132. An output signal fromfirst detector 114 is fed into gate 2 of the processor 132 and an outputsignal from second detector 128 is fed into gate 1 of the processor 132.

Either one, or both, detectors 114, 118 optionally may have coupledbetween the output(s) thereof and the processor 132 a variable resistor.This may provide a means to control the level of signal from the opticalsystems, thus allowing for calibration of the apparatus.

An alert system 134 is coupled to the processor 132. The alert systemcomprises a visual alert element (i.e. a green LED 136 and a red LED 138in the illustrated arrangement), and an audio alert element (i.e. abuzzer 140 in the illustrated arrangement). These are coupled to gates3, 4 and 5 of the processor 132. Of course, other elements may be usedin addition to, or in place of those illustrated in an alert system inother optional arrangements.

Table 1 below summarises the inputs and outputs which describe thebehaviour of the elements of the illustrated circuit when the apparatusis used in relation to banknotes.

TABLE 1 Summary of circuit element behaviour Detector Second detector128 First detector 144 (reflectance, i.e. Gate Condition (birefringence)window detection) 1 2 3 4 5 Result No note low low 0 0 1 1 0 Red lightand buzzer Non-window (e.g. low high 0 0 1 1 0 Red light printed region)and buzzer Authentic window low medium 1 0 0 0 1 Green lightNon-authentic window high medium 1 1 1 1 0 Red light (i.e. counterfeitfilm) and buzzer

The presence of a window results in a reflective signal between that ofno window and the presence of a note in intensity. Thus, the reflectancemeasuring apparatus must be able to differentiate between the threestates (i.e. no note, window region of note, or printed region of notepresent in measuring region) to enable the authentication apparatus tofunction to output a signal only when a window region of a note ispresent in the measuring region. This may be useful as a mechanism tocontrol power use of the apparatus, i.e. the presence of a window regionof a note acts as a switch to turn on the apparatus to conduct abirefringence measurement. Otherwise, the apparatus may remain (orrevert) to a standby mode.

The operation of the authentication apparatus may be summarised asfollows. Electromagnetic radiation signals (e.g. light signals) aremeasured from when the authentication apparatus is turned on. When anitem (e.g. banknote) edge enters the measuring region, there is likelyto be a fluctuation or change in the measurement readings being taken bythe reflection measuring apparatus. There is likely to be a furtherfluctuation or change when a window region of the item passes throughthe measuring region. When this occurs, the birefringence measurementperformed at that time is noted. If the birefringence measurement isrelatively low, the authentication apparatus indicates that the item isauthentic. However, if the birefringence measurement is relatively high,the authentication apparatus indicates that the item is counterfeit.Thus, an item will be deemed genuine, once a window has been detected inthe measuring region, and the birefringence measurement performed, andthe birefringence measurement value is indicative that the note isauthentic. Failure to detect any window may result in no output beinggenerated by the authentication apparatus.

FIG. 7 illustrates a device 142 which may be suitable for authenticatingbanknotes. The device 142 includes the authentication apparatus 100 inany one or more of the arrangements described above. The device 142 maybe suitable as a portable hand-held device.

The device 142 comprises a substantially U-shaped unit with a slot 144through which banknotes may be conveyed (e.g. “swiped”). Optionally, theslot depth is 40 mm (approximately half the size of larger denominationpolymer film substrate banknotes in circulation in one or morecountries). As the window region of the banknote passes thebirefringence measuring apparatus of the authentication apparatuslocated inside the device 142, the signal output by the authenticationapparatus is conveyed to an illumination device which is operative toilluminate the device with either a green or red light depending on thebirefringence reading of the window. For example, if the banknote isformed from an authentic polymer film, the device 142 may be illuminatedwith green light. However, if the banknote is formed from anon-authentic polymer film, the device 142 may be illuminated with redlight.

The dimensions of the device 142 may depend upon the size of theelectronics and power source that are required to allow the device tofunction. However, a required dimension is that of the slot height. Theslot 144 must be of sufficient depth so that, as a banknote is conveyedthrough the slot, the window of the banknote passes between theupstanding portions of the device 142 either side of the slot 144 (andthus between the elements of the birefringence measuring apparatus andthe reflectance measuring apparatus). Another required dimension will bethat of the slot width, which should be a compromise between a narrowenough slot to maintain banknote flatness during passage through theslot 144 for an accurate result and a wide enough slot to allow ease ofpassage of the banknote through the slot 144. Optionally, a slot widthof between about 0.5-1 mm may be employed. Further optionally, the slot144 may comprise curved entry and/or exit points to assist insertion ofa banknote end into the slot 144 and/or to assist removal of thebanknote from the slot 144.

FIGS. 8a and 8b illustrate another optional authentication apparatusarrangement. In this arrangement, the authentication apparatus may besuitable for banknote authentication when the banknote is static.

In this arrangement, there is provided a positioning bund 146 whichcomprises a surface for receiving the banknote thereon. The positioningbund 146 comprises a note template 148 provided thereon. For example,the note template 148 may be engraved into the surface of thepositioning bund 146 such that a recessed region is formed in thesurface of the positioning bund 146. This recessed region may be ofsimilar dimensions to a banknote and is shaped to receive a banknotetherein.

Therefore, in use, the banknote 150, comprising one or more printedsurface features 152 and a window region 154 is placed on the notetemplate 148 of the positioning bund 146 and guided into position (seearrow A) using raised edges formed at the edge of the recessed region.Elements of the authentication apparatus are located above and below thepositioning bund so as to take measurements of a portion of the banknote150 located in the measurement region 108 of the positioning bund 146.The measurement region 108 is located with respect to the positioningbund 146 so as to be coincident with the window region of a banknotewhen such a banknote is located on the positioning bund 146. Thereflectance measuring apparatus of the authentication apparatus detectswhen a window region of a banknote is in place in the measuring region108 and the authentication apparatus is then operative to performbirefringence measurement on the window region 154.

To enable the illustrated arrangement to be suitable for differentdenominations and/or different currencies (which are likely to be ofdifferent sizes), a series of banknote outline templates could beprovided (e.g. engraved) on the positioning bund. A user could hold abanknote against the appropriate banknote outline. This could be done,for example, by using raised edges at the top and either left or rightof the positioning bund 146 to guide the note into position (dependingon where the windows are more consistently positioned).

Different sizes and positions of windows could be accommodated, inoptional arrangements, by providing multiple birefringence measurementpositions.

FIGS. 9a and 9b illustrate top and side views of an authenticationapparatus according to another optional arrangement. This arrangementmay be suitable for a moving system, i.e. one where an item (e.g. abanknote) is moved relative to the authentication apparatus (or viceversa).

In the illustrated arrangement, there is shown an banknote 150 beingconveyed in a direction indicated by arrow B relative to a birefringencemeasuring apparatus 102, and through a measuring region 108. In theillustrated arrangement, the birefringence measuring apparatus 102comprises an array of birefringence measuring elements across themeasuring region width. These sensors birefringence measuring elementsare operative to indicate whether birefringence of a portion of thebanknote 150 in the measuring region 108 is high or otherwise. Theillustrated arrangement further comprises a note detector arrangement156 located adjacent to the birefringence measuring apparatus 102. Thisnote detector arrangement 156 is operative to emit, from an emitter 158,or array of emitters (item detection emitters) an electromagneticradiation beam toward the banknote transport path. A detector 160, orarray of detectors (item detection detector) are located, and operative,to receive electromagnetic radiation from said electromagnetic radiationbeam transmitted across said banknote transport path and/or reflectedfrom said transport path. Therefore, when a banknote enters the regionof the banknote transport path illuminated by the electromagneticradiation beam emitted by the emitter 158 of the note detectorarrangement 156, the presence of the banknote is detected by the notedetector arrangement 156. That is, when a banknote is present in thetransport path, the electromagnetic radiation beam emitted by emitter158 may be reflected by the banknote and received at a detector locatedto receive reflected electromagnetic radiation, or the beam may beattenuated as it passes through the banknote, and a detector located toreceive transmitted electromagnetic detection may detect a decrease inthe transmitted electromagnetic radiation being received (due topresence of the banknote in the beam). Thus, the note detectorarrangement 156 may be operative to detect presence or otherwise of thebanknote 150 by reflection of the irradiating electromagnetic radiationbeam when the banknote 150 is present and/or by a reduction in theintensity of the transmitted irradiating electromagnetic radiation beam(due to presence of the banknote in the beam). Therefore, when abanknote 150 cuts the irradiating electromagnetic radiation beam, thenote detector arrangement 156 detects the presence of the banknote 150.The note detector arrangement 156 is operative to control operation ofthe birefringence measuring apparatus 102 such that the birefringencemeasuring apparatus 102 performs measurements only when a banknote ispresent.

A reflectance measuring apparatus optionally may be present or may notbe present. In an optional arrangement without the reflectance measuringapparatus, the birefringence measuring apparatus is operative to detectlow/high birefringence readings at all times, but decisions are onlymade when the note detector arrangement presence sensor detects a note.

In such a “transmission only” arrangement, i.e. birefringencemeasurement but not reflectance measurement, the apparatus is operativeto determine that a window is present in the measuring region by notingthe signal of the detector(s) of the birefringence measurementapparatus. A background signal will result in a comparativelymedium-level output signal from the detector(s). When a printed portionof a banknote is present in the measuring region (i.e. printed regionblocks detector(s)), this will result in a comparatively low-leveloutput signal from the detector(s). When a window region of a banknoteis present in the measuring region (background signal plusbirefringence), this will result in a comparatively high-level outputsignal from the detector(s) when a counterfeit banknote is present and acomparatively low-level output signal when an authentic window ispresent. FIG. 9c illustrates the detector(s) response when variousportions of a counterfeit banknote are measured using the apparatus. Ascan be seen from FIG. 9c , when a printed portion of a banknote ispresent in the measuring region, the illuminating radiation emitted bythe emitter(s) is blocked by the printed portion of the banknote andvery little of the illuminating radiation is transmitted through thebanknote to reach the detector(s). When a window region of thecounterfeit banknote is present in the measuring region, the outputsignal from the detector(s) is comparatively high, and the apparatus isoperative to output a signal that that the banknote is counterfeit.

In optional arrangements, there may be one or two or even a complete rowof note detectors. They could be transmissive (as illustrated in FIG. 9b) or reflective. The electromagnetic radiation emitted by an emitter ofthe note detector arrangement may be white light or even a narrow bandinfra-red light.

Table 2 below illustrates a decision table for the elements of theauthentication apparatus of the optional arrangement illustrated inFIGS. 9a and 9b .

TABLE 2 Birefringence measuring Note detector Authentication apparatusoutput arrangement output apparatus output High No banknote present Nooutput Low No banknote present No output High Banknote present Fail(banknote counterfeit) Low Banknote present Banknote authentic

The arrangement of FIGS. 9a to 9c may be used in combination with thefeatures of the arrangements illustrated in FIG. 7 or FIGS. 8a and 8b ,and as described above.

The parameters which may be relevant to a reflectance measuringapparatus forming part of an authentication apparatus according to oneor more embodiments of the present invention will now be discussed.Since the reflectance measuring apparatus is operative to measure thereflected signal from a polymer surface, it is desirable that thereflections are be specular and from as narrow an angular range aspossible to ensure that only reflections from film that is in themeasurement region are accepted.

In the following description, any reference to “light” is intended toinclude electromagnetic radiation in both the “visible” part of theelectromagnetic spectrum and also the “invisible” part of theelectromagnetic spectrum.

Shade Aperture

In those arrangements in which the detector of the reflectance measuringapparatus is protected by a shade, the dimensions of a shade apertureshould be considered. In some optional arrangements, the shade aperturemay simply comprise a hole or slit in the shade. In other optionalarrangements, the shade aperture may comprise a tube which, optionally,is composed of, or lined with, a non-reflective material.

The aperture width determines the amount of electromagnetic radiationrays collected at any angle, but is indiscriminate as to the origin ofthese rays and so does not help eliminate noise from ambientelectromagnetic radiation sources or scatter.

The “set-back distance” (i.e. the distance between the second detectorand the item-side of the shade aperture—the “aperture mouth”) is relatedto the accuracy of the apparatus. A large distance between the aperturemouth and the second detector will mean that only very precisely angledlight will travel the length of the aperture tube to the seconddetector.

The set-back distance may be limited by the physical constraints of thedevice inside which a detector such as this would be fitted.

The accuracy of the apparatus may also be dependent upon the aperturewidth. That is, accuracy of the apparatus may depend on the ratio of theaperture width to the set-back distance. Therefore, in larger devices inwhich a larger set-back distance can be employed, a larger aperturewidth may be used. However, for more constrained, smaller devices, inwhich the set-back distance may be small, a narrower aperture should beused. Consequently, this will mean a reduction in the rays collected andtherefore sensitivity of the device.

The aperture of the shade is designed to exclude high angle light. Itdoes this via the use of a narrow opening with the second detectoroffset, or “set-back” from the opening. There are two optionalarrangements which may be suitable: a black tube, which will absorbstray radiation in its walls (i.e. an arrangement such as thatillustrated in FIG. 4 and as described above); and an open space behindthe aperture where high angle light will be propagated out of the rangeof the second detector.

These optional arrangements are illustrated schematically in FIGS. 10aand 10b . The optional arrangements can be simplified (for the processof performing calculations) to the arrangement illustrated in FIG. 10 c.

Referring to FIG. 10c, w is the aperture or tube width and l is theoffset or “set-back” distance of the second detector from the aperture.The tube based design may be a more efficient one when the seconddetector is wider than the aperture/tube diameter. For an aperturedesign, if the second detector is wider than the aperture, then therange of light angles that are accepted by the second detector will begreater and for the following calculations, w would become the seconddetector width.

The exception to this is the accuracy of the device, which isproportional to the entrance width for the optical system.

The angle at which light entering the system is at its maximumintensity, θ_(max) is:

$\begin{matrix}{\theta_{\max} = {\tan^{- 1}\left( \frac{w}{l} \right)}} & (1)\end{matrix}$

At angles higher than this, light rays that enter the optical system canreach only a fraction of the area of the second detector and so can beregarded as losing their intensity proportional to the angular area ofthe second detector they are incident upon.

This area, A_(z), can be calculated by first setting an exclusiondiameter, z, at the centre of the aperture's cross-sectional area. Fromz, the area of a central zone that cannot be accessed by higher anglelight can be calculated and then subsequently subtracted from theoverall slit angle to produce a result (which is effectively a ring withan inner diameter of z and an outer one of w).

The following equations show this:

$\begin{matrix}{\theta_{z} = {\tan^{- 1}\left( \frac{w + z}{l} \right)}} & (2) \\{A_{z} = {\frac{\pi}{4}\left\lbrack {w^{2} - z^{2}} \right\rbrack}} & (3)\end{matrix}$

where θ_(z) is the angle in question. If θ_(z) is plotted against A_(z)for an aperture of diameter=2 mm and a length of 10 mm and normalise theresult, the graph illustrated in FIG. 11 is obtained.

As can be seen, for a system such as this, incident light at less thanabout 11.5° will be accepted at its full intensity, which will decreaseat higher angles, dropping to zero at about 22°.

From this, it is possible to determine the maximum angle of light thatcan be accepted by the system and when the efficiency of the systembegins to decrease.

Incident Angle

In general, reflection of incident rays decreases slightly withincreased incident angle until the Brewster angle is reached) (˜44-54°,after which point reflection increases sharply. However, this is a grosssimplification for semi-transparent materials such as BOPP films orpigment filled inks used in film coatings. In reality, such materialshave many optical surfaces below the top physical one.

The presence of embedded materials such as pigments which often havesubstantially different absorbent and reflective properties will cause amaterial to have substantially different reflective properties across aseries of angles.

The angle of incidence to be used for the gloss measurement can bedetermined by considering the theoretical reflectivity of a surface forthe s and p polarisation states:

$\begin{matrix}{R_{s} = {\left\lbrack \frac{\sin\left( {\theta_{t} - \theta_{i}} \right)}{\sin\left( {\theta_{t} + \theta_{i}} \right)} \right\rbrack^{2} = \left\lbrack \frac{{n_{1}{\cos\left( \theta_{i} \right)}} - {n_{2}\;{\cos\left( \theta_{t} \right)}}}{{n_{1}{\cos\left( \theta_{i} \right)}} + {n_{2}\;{\cos\left( \theta_{t} \right)}}} \right\rbrack^{2}}} & (4) \\{R_{p} = {\left\lbrack \frac{\tan\left( {\theta_{t} - \theta_{i}} \right)}{\tan\left( {\theta_{t} + \theta_{i}} \right)} \right\rbrack^{2} = \left\lbrack \frac{{n_{1}{\cos\left( \theta_{t} \right)}} - {n_{2}\;{\cos\left( \theta_{i} \right)}}}{{n_{1}{\cos\left( \theta_{t} \right)}} + {n_{2}\;{\cos\left( \theta_{i} \right)}}} \right\rbrack^{2}}} & (5)\end{matrix}$

Where θ_(i)=incident angle, θ_(t)=transmitted angle, n₁ andn₂=refractive index of media 1 and media 2 respectively.

For a randomly polarised material, the s and p reflections are averagedtogether to obtain a theoretical reflectivity for a typical lightsource. The graph illustrated in FIG. 12 illustrates a theoreticalreflectivity of a hypothetical polypropylene surface with a refractiveindex of 1.49.

As can be seen from FIG. 12, the s polarisation state dominates thelower angles, with the p state reflecting very poorly until the Brewsterangle (tan⁻¹(n₁/n₂)=)56.3° is exceeded. The use of a non-polarised lightsource avoids the potential failure of the process at the Brewsterangle, where the signal will be zero.

In experiments to determine the viability of the reflectance measuringapparatus of the authentication apparatus, the angles used were about45° to about 60°. Using such angles, the reflectivity was between about5% and about 9%.

As noted above, the reflectivity of the printed areas will be morecomplex due to the presence of pigmented material under the surface.Firstly, if the surface of the printed area is as flat as thenon-printed area, then the overall reflectance could be calculated usingequations (4) and (5) but with an additional value that takes intoaccount the reflectivity of pigments under the surface of the ink. Aspigments are generally small and well dispersed, this is taken to be areasonable assumption.

Pigments are designed to absorb parts of the electromagnetic spectrumand reflect others. An ideal pigment will reflect as much light as itcan whilst still maintaining its target colour—otherwise it will bequite dull. Conveniently, for the process performed by the apparatus ofone or more embodiments of the present invention, both pigments ingeneral and especially banknote pigments are dull. Coupled with this,pigments reflect light in all directions (otherwise it would not bepossible to see them unless they are viewed at an angle equal to theincident angle of the ambient light in the environment). This meansthat, at any one angle, only a portion of the reflected light is seen.Add these two factors together and it means that a great deal ofdifference between the reflectivities of the printed and unprinted areaswould not be expected, except at low angles)(<30° where pigmentreflection will make the printed areas reflect more and at anglesgreater than the Brewster angle, when top surface (and bottom surface inthe case of unprinted film) reflections are expected to dominate overpigment reflections making the unprinted areas more reflective.

In an experiment to measure gloss using the reflectance measuringapparatus forming part of the authentication apparatus according to oneor more embodiments of the present invention, an Australian $50 banknotewas passed through the measuring region of the reflectance measuringapparatus to mimic a banknote sorting system.

FIG. 13 illustrates the intensity profile detected when the Australian$50 banknote is passed through the reflectance measuring apparatusforming part of the authentication apparatus according to one or moreembodiments of the present invention.

In the figure, the straight line X illustrates where the apparatusscanned the banknote, and the other line Y illustrates the voltagesignal output by the second detector of the reflectance measuringapparatus.

The pigmented regions of the note reflect more (although not much more)than the window region Z, and are not affected much by the colour of thenote (although the colours on this particular note are relativelyplain). This experiment was conducted at an angle 60°, where a 9%reflectivity from the film would be expected. If the angle is reduced,then the importance of the pigment in the reflection will increase andvice versa.

It is clear from the graph that the edge of the note can be detected(i.e. the steep increase of the curve (denoted by Y₁) at the right-handside of the figure). Also, the window region Z of the note can bedetected-note the decrease in the voltage profile (denoted by Y₂) whichis coincident with the location of the window region Z.

Second Detector “Stand-Off” Distance/Divergence/Second Detector Signal

Light from most sources is highly divergent (the exceptions being laserlight and starlight) and therefore any ideal incident ray/reflected raymodels quickly break up with increased distance of the second detectorfrom the point of reflection. The centre of any divergent light sourcewill still contain the ideal rays, but the greater the distance of thesecond detector from the point of reflection, the less intense thereceived reflected rays will be.

Therefore, it will be appreciated that increased divergence ofilluminating rays and/or increased distance of the second detector fromthe point of reflection will decrease the signal strength of the readingfrom the second detector because the intensity of the received reflectedrays will be less.

However, if a second detector is close to a surface (and thus, the pointof reflection) then it will gather light from a broader range of angles.This may lead to the second detector receiving unwanted rays and thusaffect the value of the signal output by the second detector.

Reflectance measuring apparatus forming part of the authenticationapparatus according to one or more embodiments of the present inventionmay require the second detector to collect reflected rays from preciseangles.

It will be appreciated from the above, therefore, that increasing thedistance between the second detector and an item surface will increaseits accuracy (because the likelihood of the second detector gatheringlight from a broader range of angles is reduced). However, increasingthe distance between the second detector and an item surface will alsoreduce the intensity of reflected rays received by the second detector.

Additionally, decreasing divergence of the illuminating source (i.e. thesecond emitter) will also increase accuracy of the reflectance measuringapparatus as the decreased divergence may result in fewer strayreflections. Therefore, in an optional arrangement, the second emittercomprises a laser light source.

Photodiodes generate a voltage that is proportional to the intensity oflight that falls upon them. The intensity of light (which must not beconfused with radiant intensity) can be calculated from the irradianceof a light source which is given by:

$\begin{matrix}{I_{o} = \frac{P\;\pi\; d^{2}}{4}} & (6)\end{matrix}$

where I_(o) is the irradiance (W/mm²) at the light source, P is thepower of the light source (W) and d is the diameter of the light source(mm).

However, it is the irradiance at the second detector rather than thesource (i.e. the second emitter) that is of interest. To establish this,the path length between the light source and the second detector(collectively the “probes”) must be calculated. The relationship betweenpath length, l_(path), and stand-off distance, z_(probe), is as follows:

$\begin{matrix}{l_{path} = \frac{2z_{probe}}{\cos\;\theta_{probe}}} & (7)\end{matrix}$

where θ_(probe) is the angle at which the light source and the seconddetector are set relative to the surface (the angle between the two willbe double this). This distance is the distance between light source andsecond detector.

The diameter of the beam at the second detector (e.g. photodiode),d_(photo), can be calculated by the following:d _(photo) =d+2l _(path) tan θ_(div)  (8)

where d is the diameter of the light source and θ_(div), is thedivergence of the light source (which will be quoted as part of thetechnical specification of the light source).

The intensity at the second detector can then be calculated as:

$\begin{matrix}{I_{div} = {\frac{P\;\pi\; d_{photo}^{2}}{4} = \frac{P\;{\pi\left( {d + {2l_{path}\tan\;\theta_{div}}} \right)}}{4}}} & (9)\end{matrix}$

The intensity drop between source and second detector can therefore becalculated by:

$\begin{matrix}{{{Intensity}\mspace{14mu}{Drop}} = {\frac{I_{div}}{I_{o}} = \frac{d_{photo}^{2}}{d^{2}}}} & (10)\end{matrix}$

Any calculation of stand-off distance must therefore take into accountthe drop off in intensity from the light source to the second detectorwhich is a product of the angles involved and the path lengths of thelight. The limits of this will be determined by the light sourceintensity, the second detector sensitivity and the ambient light noiselevels.

The light emitted by the light source has three separate conditions withrespect to the second detector:

-   -   If d_(photo)>w, then the second detector is too far from the        measuring region and useful low angle light is being lost.    -   If d_(photo)=w, then the second detector is at the correct        distance from the measuring region.    -   If d_(photo)<w, then the second detector is too close to the        measuring region and higher angle light than the second detector        is designed to accept can find its way into the second detector.

Equations (7) and (8) can be rearranged to give equations (11) and (12)which show how the optimal stand-off distance, Z_(probe), can becalculated for a divergence angle and a device angle (11); and how theoptimal device angle can be calculated for a stand-off distance anddivergence angle (12):

$\begin{matrix}{z_{probe} = \frac{\left( {w - d} \right)\cos\;\theta_{probe}}{4\;\tan\;\theta_{div}}} & (11) \\{\theta_{probe} = {\cos^{- 1}\left( \frac{4z_{probe}\tan\;\theta_{div}}{\left( {w - d} \right)} \right)}} & (12)\end{matrix}$

From (11), it may be appreciated that, the lower the light sourcedivergence, the further the possible stand-off distance.

Resolution of the Edge Detection

Another consideration with the reflectance measuring apparatus formingpart of the authentication apparatus according to one or moreembodiments of the present invention may be the accuracy of the edgedetection, which is a function of the size of w, i.e. the size ofentrance aperture/tube diameter. In practice, the resolution ofdetection will be slightly smaller than the aperture size as thereflected light will diverge as it travels from the film to theaperture.

First, the path length must be calculated. This uses a similar equationto that shown in equation (7). However, this path length is from thesurface of the film only and from the aperture to the film instead offrom the film to the detector:

$\begin{matrix}{l_{reflected} = \frac{z_{aperture}}{\cos\;\theta_{probe}}} & (13)\end{matrix}$

where l_(reflected) is the reflected path length and z_(aperture) is thedistance between the film surface and the aperture.

From this, it is possible to calculate the width of the ray, d_(res)that would be accepted by an aperture of d_(aperture) width and over apath length of l_(ref). The method is the reverse of equation (8),substituting in the new widths and path lengths that describe thereflected light:d _(res) =d _(aperture)−2l _(ref) tan θ_(div)  (14)

The resolution would therefore be greater than the aperture—which couldbe considered as the minimum resolution of the system.

Wavelength

Wavelength of the illuminating rays may alter the behaviour ofreflections with respect to surface roughening (i.e. alteredinterference).

In an optional arrangement, an IR emitter is used. This may improveaccuracy of the apparatus because the second detector in such anarrangement is IR ray sensitive and so may be unaffected by interferencefrom ambient light sources. However, in other optional arrangements,second emitters operative to emit electromagnetic radiation from otherparts of the electromagnetic spectrum may be suitable. In such cases,the second detector may be protected from stray rays by, for example, ashade.

Item or Bank Note Angle

Although in the ideal situation, the angle of the item or banknote tothe second detector will always be the same, in reality this will notalways be the case. For example, the banknote may contain creases, ordraughts may cause “flutter” of the note in the measuring region.Variations in note to second detector angle will alter the angle of thedesired reflection. To counter this, the angular range of seconddetector acceptance can be increased (through shortening the set-backdistance). However, this may decrease the accuracy of the device, so asuitable balance between these conflicting parameters will need to beachieved.

The variance in the reflectivity angle caused by the above-describedexample phenomena may be plus or minus a few degrees. Such a variancecould be accounted for in an optional arrangement by employing aninterpretation module in the apparatus to effectively remove seconddetector readings caused due to variance in reflectivity angle.

FIG. 14 schematically illustrates a top view of an emitter-detector-itemarrangement of the reflectance measuring apparatus for use in anoptional arrangement of the authentication apparatus of one or moreembodiments of the present invention. To aid clarity, a birefringencemeasurement apparatus of the authentication apparatus is not shown.

The reflectance measuring apparatus 300 comprises a second emitter 302,second detector 304, processing means 306 electronically coupled tosecond detector 304 by signal line 308, and a shade 310 associated withthe second emitter 302 and second detector 304. The shade 310 will bedescribed in more detail later.

The reflectance measuring apparatus 300 is configured such that thesecond emitter 302 and second detector 304 are oriented to face ameasuring region 311. Second emitter 302 is operative to illuminate themeasuring region 311 with electromagnetic radiation (denoted by dottedarrow IL in the figure), and second detector 304 is oriented andoperative to receive electromagnetic radiation (denoted by dotted arrowRL in the figure) reflected from a portion of an item located in themeasuring region 311.

Optionally, the authentication apparatus may comprise a path along whichan item may be conveyed. The measuring region 311 forms part of thispath. Thus, in this particular arrangement, the item may be conveyedalong the path from one side of the authentication apparatus to theother and, during its transit, pass through the measuring region 311.

In the illustrated arrangement, the item comprises a banknote 312.

The shade 310 in the illustrated arrangement comprises a main bodyelement in which are provided a second emitter tube 314 a and a seconddetector tube 314 b. The second emitter 302 is located at, or near, oneend of second emitter tube 314 a on a first side of the shade 310. Thesecond detector 304 is located at, or near, one end of second detectortube 314 b on the first side of the shade 310. Illuminatingelectromagnetic radiation IL emitted by second emitter 302 travelsthrough second emitter tube 314 a and emerges from the second emittertube 314 a at a mouth portion thereof. The mouth portion is located on asecond side of the shade 310. Second detector tube 314 b is located andoriented within the shade 310 relative to the second emitter tube 314 aand measuring region 311 such that reflected electromagnetic radiationRL reflected from the measuring region 311 enters second detector tube314 b at a mouth portion thereof. The mouth portion of the seconddetector tube 314 b is located on a second side of the shade 310. Afterentering the second detector tube 314 b via mouth portion, the reflectedelectromagnetic radiation RL travels along second detector tube 314 b tosecond detector 304.

In operation, the banknote 312 will be conveyed along the path in adirection from the left-hand side to the right-hand side of the figure(i.e. as indicated by arrow C). The instance illustrated in FIG. 14shows the banknote 312 with a portion thereof located in the measuringregion 311. Illuminating electromagnetic radiation IL from secondemitter 302 passes through second emitter tube 314 a and exits thesecond emitter tube 314 a from the mouth portion thereon. After exitingthe second emitter tube 314 a, the illuminating electromagneticradiation IL is incident upon the portion of the banknote 312 located inthe measuring region 311. At least a portion of the incidentilluminating electromagnetic radiation IL will be reflected by thebanknote 312. This reflected electromagnetic radiation RL is reflectedtoward mouth portion of second detector tube 314 b, from where it enterssecond detector tube 314 b and continues thereafter to second detector304. The second detector 304, responsive to detection of reflectedelectromagnetic radiation RL incident thereon, outputs a signalproportional to the intensity of received reflected electromagneticradiation RL via signal line 308 to processing means 306.

Processing means 306, upon receiving an output signal from the seconddetector 304, is operative to compare a value of the received signalwith a set of pre-defined values stored in a database (not shown). Thesepre-defined values may correspond to expected reflected electromagneticradiation values when one or more of: a printed region of a banknote islocated in the measuring region 311; an unprinted region of a banknote(e.g. a window region) is located in the measuring region 311; nobanknote is located in the measuring region 311. The processing meansmay use this signal, in conjunction with a signal received from thebirefringence measuring apparatus (not shown) to output a signalindicative of whether or not the banknote is authentic or not.

As the banknote 312 continues its passage through the reflectancemeasuring apparatus 300, the processing means 306 receives a number ofreadings from the second detector 304. Optionally, the birefringencemeasuring apparatus performs its measurement only when a window regionis located in the measuring region 311 (i.e. the operation of thebirefringence measurement may be based on the signal output by thereflectance measuring apparatus).

This apparatus 300 may form part of an authentication apparatusimplemented in, for example, a banknote counting system. The processingmeans 306 may be operative to output a signal to a counting device onlywhen a genuine banknote passes through the authentication apparatus.

In optional arrangement, the shade 310 may comprise an injection mouldedpart (optionally a single injection moulded part) which, furtheroptionally, comprises an absorbent black pigmented polymer such as, forexample, polyethylene, nylon or polypropylene.

The second emitter 302 may optionally comprise an LED and/or a laser ofa number of different wavelengths. Optionally, the wavelength of theilluminating electromagnetic radiation IL may be in the IR region of theelectromagnetic spectrum, e.g. about 890 nm.

The second detector 304 may optionally comprise a photodiode configuredto provide a broad spectrum second detector (e.g. operative to detectreflected rays having wavelengths in the range of about 400 nm to about1140 nm). In a particular optional arrangement, the second detector maybe operative to detect reflected rays having wavelengths in the range ofabout 880 nm to about 1140 nm.

FIG. 15 schematically illustrates a top view of an emitter-detector-itemarrangement of the reflectance measuring apparatus for use in anoptional arrangement of the authentication apparatus of one or moreembodiments of the present invention. Again, to aid clarity, abirefringence measurement apparatus of the authentication apparatus isnot shown.

Features similar to those illustrated in FIG. 14 are also illustrated inFIG. 15. In FIG. 15, the features common with those FIG. 8 are nowdesignated with reference numerals of the type 4XX rather than 3XX.Thus, in FIG. 15, the reflectance measuring apparatus is denoted byreference number 400 (rather than 300), the second emitter, by referencenumber 402 (rather than 402) and so on.

The arrangement illustrated in FIG. 15 is similar to that of FIG. 14except for the replacement of a single second emitter and single seconddetector with multiple second emitters and multiple second detectors.Thus, in FIG. 15, three second emitters 402 a, 402 b, 402 c replace thesingle second emitter 302 of the arrangement illustrated in FIG. 14, andthree second detectors 404 a, 404 b, 404 c replace the single seconddetector 304 of the arrangement illustrated in FIG. 14.

A first one of the second emitters 402 a is paired with a first one ofthe second detectors 404 a, a second one of the second emitters 402 b ispaired with a second one of the second detectors 404 b, and a third oneof the second emitters 402 c is paired with a third one of the seconddetectors 404 c.

In view of the increase in the number of second emitters and seconddetectors compared with the arrangement illustrated in FIG. 14,consequent modifications are also required to the shade. Thus threesecond emitter tubes 414 a, 414 a′ and 414 a″ are provided in shade 410,along with three second detector tubes 414 b, 414 b′, 414 b″.

Illuminating electromagnetic radiation IL emitted by the first one ofthe second emitters 402 a will travel along a first one of the secondemitter tubes 414 a and be incident upon a portion of the banknote 412in the measuring region 411. Reflected electromagnetic radiation RLreflected from the banknote 412 in the measuring region 411 will traveltoward a mouth of a first one of the second detector tubes 414 b and,upon entering the first one of the second detector tubes 414 b throughthe mouth thereof, will travel along the first one of the seconddetector tubes 414 b to be received by the first one of the seconddetectors 404 a.

Similarly, illuminating electromagnetic radiation IL emitted by thesecond one of the second emitters 402 b will travel along a second oneof the second emitter tubes 414 a′ and be incident upon a portion of thebanknote 412 in the measuring region 411. Reflected electromagneticradiation RL reflected from the banknote 412 in the measuring region 411will travel toward a mouth of a second one of the second detector tubes414 b′ and, upon entering the second one of the second detector tubes414 b′ through the mouth thereof, will travel along second one of thesecond detector tubes 414 b′ to be received by the second one of thesecond detectors 404 b.

Further, the third one of the second emitters 402 c is operative to emitlight into a third one of the second emitter tubes 414 a″. Raysreflected from the portion of the banknote 412 in the measuring region411 due to incidence of illuminating electromagnetic radiation IL fromthe third one of the second emitter tubes 414 a″ will travel toward amouth of the third one of the second detector tubes 414 b″ and, uponentering the third one of the second detector tubes 414 b″ through themouth thereof, will travel along the third one of the second detectortubes 414 b″ to be received by the third one of the second detectors 404c.

Thus, in the illustrated optional arrangement, the reflectance measuringapparatus 400 comprises a multiple angle point analysis apparatus.

As described above, the second emitters are matched in their aperturepaths with the second detectors. Although in this instance there arethree angles shown for both second emitter and second detector, morecould be used in other optional arrangements if appropriate.

The second emitters 402 a, 402 b, 402 c are oriented so thatilluminating electromagnetic radiation emitted therefrom is incident onthe same part of the surface of the item being detected, i.e. the samepoint in the measuring region. It follows that the second detectors 404a, 404 b, 404 c should be similarly oriented in order to receiveelectromagnetic radiation reflected from the same part of the surface.

The processor 406 may be operative to perform analysis of multipleoutput signals received from the second detectors 404 a, 404 b, 404 c.

In another optional arrangement, reflection measurement using multiplewavelengths could be applied to single or multiple angle measurements(i.e. the apparatus illustrated in FIG. 14 or 15 could be configured tomake reflection measurements over a number of different wavelengths).

Possible configurations which could be based on the same geometry as thesingle wavelength measurement devices may comprise:

a) Colour second emitter to second detector: a single coloured secondemitter replaces the second emitter in the arrangement of FIG. 14.However, if more than one colour was to be employed at a particularangle, this may prove problematic. There may be two solutions, namely:

-   -   i. rotating the measurement around a circle: this maintains the        angle and measures the same point of the note at the same time,        but risks variation due to polarisation by reflection. The        differences are not likely to be extreme and, if the same        measurement orientation is used every time, the results will be        consistent; and    -   ii. delayed signals: measurement of points in a line could be        measured in a cascading sequence by rows of parallel detection        systems (point 1 is measured by station 1 at time 1, point 1 is        measured by station 2 at time 2 whilst point 2 is being measured        by station 1, etc.)

b) A white light emitter source may be used in conjunction with one ormore of:

-   -   i. a spectrometer in place of the photodiode second detector;    -   ii. the functional components of a spectrometer located in the        aperture tube (i.e. diffraction grating and a CCD second        detector/CMOS); and    -   iii. a digital camera.

Another optional arrangement of one or more embodiments of the presentinvention comprises a reflectance measuring apparatus operative toperform a full area scan. Such an arrangement is illustrated in FIG. 15.In this arrangement, there is provided a reflectance measuring apparatus500 which comprises a strip electromagnetic radiation source 502operative to emit illuminating electromagnetic radiation IL toward abanknote 506 located in the authentication apparatus. The incidentelectromagnetic radiation IL may be reflected by the note as reflectedelectromagnetic radiation RL toward a line-scan camera 504.

In this arrangement, the mode of operation is the same as described inother arrangements above, except that the second emitter/second detectorcombination of the earlier described arrangement is replaced with stripelectromagnetic radiation source 502 and line-scan camera 504. Thebanknote 506 may be moved relative to the strip electromagneticradiation source 502 and line-scan camera 504 or vice versa. Such anarrangement may be used to obtain a full map of the surface reflectivityat a particular illumination angle by taking measurements of the valueof the reflected electromagnetic radiation RL using line-scan camera504.

This map may optionally be monochrome or coloured (i.e. reflectedelectromagnetic radiation RL is collected by way of a colour camera orvia a diffraction grating coupled to a 2D CMOS array). Further, the mapmay be built up from a series of measurements obtained by illuminatingthe banknote over a series of angles (e.g. similar to the arrangementillustrated in FIG. 15, but with the strip electromagnetic radiationsources and line-scan cameras effectively extending into/out of theplane of the paper).

In an optional arrangement, IR light just outside the visible spectrummay be used. In a further optional arrangement, one way of potentiallyreducing noise would be to employ a filter to filter out white light.

In all of the above-described “non-static” arrangements, a banknote maybe moved relative to the authentication apparatus (i.e. moved along atransport path through the apparatus). However, in other optional“non-static” arrangements, the banknote may be stationary and theapparatus moved relative to the banknote.

In another optional arrangement, the emitter(s) and detector(s) of thebirefringence measuring apparatus may be tilted or offset so that theoptical path-length through the note increases.

In the above described arrangements, the polarisers of the birefringencemeasuring apparatus are “crossed”. That is, a first polariser 112 isarranged such that a transmission orientation thereof is about ±45° to atransmission orientation of a portion of an item 106 located in ameasuring region 108. A second polariser 116 is arranged such that atransmission orientation thereof is about ±45° to the transmissionorientation of the portion of the item 106 located in the measuringregion 108. That is, the transmission orientation of the first polariser112 is at about 90° to that of the second polariser 116. In an optionalarrangement, the transmission orientation of the first polariser 112 tothat of the second polariser 116 may be 90°. However, in other optionalarrangements, the transmission orientation of the first polariser 112 tothat of the second polariser 116 may be non-perpendicular. For example,the transmission orientation of the first polariser 112 to that of thesecond polariser 116 may be about 89°. In such “non-perpendicular”arrangements, the amount of illuminating radiation which is allowed topass through the polarisers increases compared with the “perpendicular”arrangements. This will affect the background levels of the detector(s)and may improve the ability of the apparatus to detect edges.

Insofar as embodiments of the invention described above areimplementable, at least in part, using a software-controlledprogrammable processing device such as a general purpose processor orspecial-purposes processor, digital signal processor, microprocessor, orother processing device, data processing apparatus or computer system itwill be appreciated that a computer program for configuring aprogrammable device, apparatus or system to implement the foregoingdescribed methods and apparatus is envisaged as an aspect of the presentinvention. The computer program may be embodied as any suitable type ofcode, such as source code, object code, compiled code, interpreted code,executable code, static code, dynamic code, and the like. Theinstructions may be implemented using any suitable high-level,low-level, object-oriented, visual, compiled and/or interpretedprogramming language, such as, Liberate, OCAP, MHP, Flash, HTML andassociated languages, JavaScript, PHP, C, C++, Java, BASIC, Perl,Matlab, Pascal, Visual BASIC, JAVA, ActiveX, assembly language, machinecode, and so forth. A skilled person would readily understand that term“computer” in its most general sense encompasses programmable devicessuch as referred to above, and data processing apparatus and computersystems.

Suitably, the computer program is stored on a carrier medium in machinereadable form, for example the carrier medium may comprise memory,removable or non-removable media, erasable or non-erasable media,writeable or re-writeable media, digital or analog media, hard disk,floppy disk, Compact Disk Read Only Memory (CD-ROM), Company DiskRecordable (CD-R), Compact Disk Rewriteable (CD-RW), optical disk,magnetic media, magneto-optical media, removable memory cards or disks,various types of Digital Versatile Disk (DVD) subscriber identitymodule, tape, cassette solid-state memory.

As used herein any reference to “one embodiment” or “an embodiment”means that a particular element, feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. The appearances of the phrase “in one embodiment” in variousplaces in the specification are not necessarily all referring to thesame embodiment.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive or and not to an exclusive or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

In addition, use of the “a” or “an” are employed to describe elementsand components of the invention. This is done merely for convenience andto give a general sense of the invention. This description should beread to include one or at least one and the singular also includes theplural unless it is obvious that it is meant otherwise.

In view of the foregoing description it will be evident to a personskilled in the art that various modifications may be made within thescope of the invention.

The scope of the present disclosure includes any novel feature orcombination of features disclosed therein either explicitly orimplicitly or any generalisation thereof irrespective of whether or notit relates to the claimed invention or mitigate against any or all ofthe problems addressed by the present invention. The applicant herebygives notice that new claims may be formulated to such features duringprosecution of this application or of any such further applicationderived therefrom. In particular, with reference to the appended claims,features from dependent claims may be combined with those of theindependent claims and features from respective independent claims maybe combined in any appropriate manner and not merely in specificcombinations enumerated in the claims.

The invention claimed is:
 1. An item authentication system comprising: abirefringence measuring apparatus comprising a measuring region, whereinthe birefringence measuring apparatus measures a birefringencecharacteristic in a test item portion comprising a film substrate whenpresent in the measuring region and produces a birefringence outputsignal corresponding to the measured birefringence; an item detectionapparatus that measures a characteristic in the test item portion andproduces an output signal corresponding to the measured characteristicindicative of the test item being present in the measuring region; aprocessor that: (i) receives the birefringence output signal from thebirefringence measuring apparatus and compares a value of the receivedbirefringence output signal to one or more predetermined values; and(ii) generates one or more determination signals indicating whether thetest item is authentic or not authentic based on the comparison; and aprocessor that: (i) receives the item detection output signal from theitem detection apparatus and compares a value of the received outputsignal to one or more predetermined values; (ii) generates one or moreitem detection signals indicating whether the test item is located inthe measuring region; and (iii) outputs a determination signal to acontrol means indicative of the presence of the test item in themeasuring region, wherein responsive to receipt thereof, the controlmeans outputs an authenticity signal indicative of authenticity ornon-authenticity of the test item based on the determination signalsindicating whether the test item is authentic or not authentic, whereinthe processor receiving the birefringence output signal and theprocessor receiving the item detection output signal may be the sameprocessor or different processors.
 2. The apparatus according to claim1, further comprising an alert system that is activated by a processorwhen a determination of authenticity or non-authenticity has been made.3. The apparatus according to claim 1, wherein the test item portion isopaque, semi-opaque, transparent region, or semi-transparent.
 4. Theapparatus according to claim 1, wherein the test item portion is opaque,semi-opaque, transparent region, or semi-transparent.
 5. The apparatusaccording to claim 1, wherein at least part of the measuring regioncomprises a transport path along which the test item is conveyable. 6.The apparatus according to claim 1, wherein the test item is a banknote.7. A banknote counting apparatus comprising the authentication system ofclaim 1, wherein the banknote counting apparatus counts banknotesconveyed through the apparatus and receives an output signal to countbanknotes only when the output signal indicates that a test item in themeasuring region is authentic.
 8. The apparatus according to claim 7,wherein the note counting device alters the note count by incrementingthe count.
 9. The apparatus according to claim 1, wherein thebirefringence measuring apparatus comprises: a birefringence measurementemitter that illuminates the measuring region with electromagneticradiation; a first polariser located between the birefringencemeasurement emitter and a first side of the measuring region so thatelectromagnetic radiation emitted by the birefringence measurementemitter passes therethrough; a birefringence measurement detectorlocated on a second side of the measuring region, wherein thebirefringence measurement detector receives electromagnetic radiationtransmitted through the measuring region from the birefringencemeasurement emitter and produces an outputted birefringence signalcorresponding to a measured birefringence characteristic; and a secondpolariser located between the second side of the measuring region andthe birefringence measurement detector so that electromagnetic radiationtransmitted through the measuring region passes therethrough, whereinthe second polariser is oriented so as to effect polarisation in adirection transverse to that of the first polariser.
 10. The apparatusaccording to claim 9, wherein the birefringence signal is proportionalto an intensity of transmitted electromagnetic radiation received. 11.The apparatus according to claim 9, wherein the birefringencemeasurement emitter comprises a light source.
 12. The apparatusaccording to claim 11, wherein the light source comprises a white lightemitting LED.
 13. The apparatus according to claim 9, wherein thebirefringence measurement detector comprises a photodetector.
 14. Theapparatus according to claim 13, wherein the photodetector comprises aphotodiode.
 15. The apparatus according to claim 14, wherein thephotodiode is suitable for detecting white light.
 16. The apparatusaccording to claim 9, wherein the birefringence measurement emitter isslidably mounted on a rail or rod.
 17. The apparatus according to claim16, wherein the birefringence measurement emitter is attached to therail or rod by an attachment which is slidable relative to the rail orrod, and which attachment comprises a fixing element to allow a positionof the birefringence measurement emitter to be fixed relative to therail or rod.
 18. The apparatus according to claim 9, wherein thebirefringence measurement detector is slidably mounted on a rail or rod.19. The apparatus according to claim 18, wherein the birefringencemeasurement detector is attached to the rail or rod by an attachmentwhich is slidable relative to the rail or rod, wherein the attachmentcomprises a fixing element to allow a position of the birefringencemeasurement detector to be fixed relative to the rail or rod.
 20. Theapparatus according to claim 1, wherein the item detection apparatuscomprises: a reflectance measurement emitter that illuminates the testitem with electromagnetic radiation in the measuring region; and areflectance measurement detector that receives electromagnetic radiationreflected from the item detection region, measures the intensity of thereflected electromagnetic radiation, and communicates a reflectanceoutput signal to the processor receiving the item detection outputsignal.
 21. The apparatus according to claim 20, wherein the reflectanceoutput signal is proportional to an intensity of reflectedelectromagnetic radiation received.
 22. The apparatus according to claim20, wherein the reflectance measurement detector has associatedtherewith a shade comprising an aperture, wherein localization of theaperture relative to the reflectance measurement detector permitselectromagnetic radiation reflected from the portion of the test item tobe received by the reflectance measurement detector.
 23. The apparatusaccording to claim 22, wherein the shade comprises a tube and theaperture comprises a hollow portion of the tube.
 24. The apparatusaccording to claim 23, wherein the reflectance measurement detector islocated at an end of the tube, or within the tube.
 25. The apparatusaccording to claim 22, wherein the aperture comprises a tubular regionin the shade.
 26. The apparatus according to claim 25, wherein thereflectance measurement detector is located at an end of, or within, thetubular region of the shade.
 27. The apparatus according to claim 20,wherein the reflectance measurement emitter has associated therewith ashade comprising an aperture, wherein localization of the aperturerelative to the reflectance measurement detector permits electromagneticradiation emitted from the reflectance measurement emitter to bedirected toward the measuring region of the apparatus.
 28. The apparatusaccording to claim 27, wherein the shade comprises a tube, and whereinthe aperture comprises a hollow portion of the tube.
 29. The apparatusaccording to claim 28, wherein the reflectance measurement emitter islocated at an end of the tube, or within the tube.
 30. The apparatusaccording to claim 27, wherein the aperture comprises a tubular regionin the shade.
 31. The apparatus according to claim 30, wherein thereflectance measurement emitter is located at an end of, or within, thetubular region of the shade.
 32. The apparatus according to claim 20,wherein the reflectance measurement emitter emits coherentelectromagnetic radiation.
 33. The apparatus according to claim 20,wherein the reflectance measurement emitter comprises at least one LED.34. The apparatus according to claim 33, wherein the at least one LEDemits light in the infra-red range of the electromagnetic spectrumand/or comprises a white light emitter source.
 35. The apparatusaccording to claim 20, wherein the reflectance measurement emittercomprises at least one strip electromagnetic radiation source.
 36. Theapparatus according to claim 20, wherein the reflectance measurementdetector comprises at least one photodiode.
 37. The apparatus accordingto claim 36, wherein the at least one photodiode detects light in theinfra-red range of the electromagnetic spectrum.
 38. The apparatusaccording to claim 20, wherein the reflectance measurement detectorcomprises at least one line-scan camera, or comprises at least onespectrometer in combination with a CCD image sensor or a CMOS imagesensor.
 39. The apparatus according to claim 20, wherein the reflectancemeasurement emitter comprises at least one plurality selected from thegroup consisting of a plurality of LEDs; a plurality of white lightemitter sources; and a plurality of strip electromagnetic radiationsources; wherein the reflectance measurement detector comprises at leastone plurality selected from the group consisting of a plurality ofphotodiodes; a plurality of line-scan cameras; and a plurality ofspectrometers, wherein each spectrometer is combined with a CCD imagesensor or a CMOS image sensor; wherein each of the plurality of LEDs,white light emitter sources and strip electromagnetic radiation sourcesis paired with a photodiode, line-scan camera, or spectrometer combinedwith a CCD image sensor or a CMOS image sensor.
 40. The apparatusaccording to claim 39, comprising a plurality of LEDs, wherein at leastone of the plurality of LEDs emits light in the infra-red range of theelectromagnetic spectrum.
 41. The apparatus according to claim 39,comprising a photodiode that detects light in the infra-red range of theelectromagnetic spectrum.
 42. A method of authenticating a test itemcomprising the steps of: (a) placing or conveying a test item portioncomprising a film substrate into or through a measuring region in abirefringence measuring apparatus; (b) measuring a birefringencecharacteristic in the test item portion and producing a birefringenceoutput signal corresponding to the measure birefringence; (c) measuringa characteristic in the test item portion and producing an output signalcorresponding to the measured characteristic indicating that the testitem is present in the measuring region; (d) transmitting thebirefringence output signal to a processor that compares a value of thereceived birefringence output signal to one or more predeterminedvalues; (e) generating one or more determination signals indicatingwhether the test item is authentic or not authentic based on thecomparison; (f) transmitting the output signal in step (c) to aprocessor that compares a value of the received output signal to one ormore predetermined values; (g) generating one or more item detectionsignals indicating whether the test item is present in the measuringregion; and (h) outputting a determination signal to a control meansindicating the presence of the test item portion in the measuringregion, wherein responsive to receipt thereof, the control means outputsan authenticity signal indicative of authenticity or non-authenticity ofthe test item based on the determination signals indicating whether thetest item is authentic or not authentic, and wherein the processorreceiving the birefringence output signal and the processor receivingthe item detection output signal may be the same processor or differentprocessors.
 43. The method according to claim 42, further comprising thestep of activating an alert system when a determination of authenticityor non-authenticity has been made.
 44. The method according to claim 42,comprising determining whether the film substrate in the test item ismade by a bubble process or by a different process.
 45. The methodaccording to claim 42, wherein a transport path is provided to themeasuring region and one or more test items are conveyed along the path.46. The method according to claim 42, wherein the step of measuring thebirefringence comprises the steps of: illuminating the measuring regionwith electromagnetic radiation from a birefringence measurement emitter;and receiving electromagnetic radiation transmitted through the testitem portion in the measuring region into a birefringence measurementdetector; and measuring the birefringence characteristic in the testitem portion based on receipt of the electromagnetic radiation by thebirefringence measurement detector.
 47. The method according to claim46, comprising: positioning a first polarizer between the birefringencemeasurement emitter and a first side of the measuring region so thatelectromagnetic radiation emitted by the birefringence measurementemitter passes therethrough; positioning the birefringence measurementdetector on a second side of the measuring region and a second polarizerbetween the measuring region and the birefringence measurement emitterso that electromagnetic radiation transmitted through the measuringregion passes therethrough; orienting the second polariser so as toeffect polarisation in a direction transverse to that of the firstpolariser; and outputting the birefringence output signal from thebirefringence measurement detector corresponding to the measuredbirefringence characteristic.
 48. The method according to claim 47,wherein the test item portion is opaque, semi-opaque, transparentregion, or semi-transparent.
 49. The method according to claim 42,wherein step (c) comprises the steps of: illuminating the measuringregion with electromagnetic radiation from a reflectance measurementemitter; receiving electromagnetic radiation reflected from the testitem portion in the measuring region into a reflectance measurementdetector; and measuring the reflectance characteristic in the test itemportion based on receipt of the electromagnetic radiation by thereflectance measurement detector.
 50. The method according to claim 49,wherein the test item portion is opaque, semi-opaque, transparentregion, or semi-transparent.
 51. The method according to claim 42,wherein the test item is a banknote.
 52. The method according to claim51, further comprising the step of counting banknotes conveyed throughthe authentication system into a banknote counting device, wherein thebanknote counting device receives an output signal from the processorand counts a banknote only when the output signal indicates that a testitem in the measuring region is authentic.
 53. The method according toclaim 52, comprising altering the banknote count by incrementing thecount.